Every time i open my diffs there is very little oil in there even though i filled them up OK.It doesn't matter if i filled them up yesterday or a week ago.And the weird is that i don't see any signs of silicone oil outsite of the case.
Anyway i'm switching to grease since i allready use 3/3/1 oil so with the right f=grease i think i can get it close.
What's the differences in performance when using grease in the diffs?

Man, I would go the other way if I was u...that oil must be going somewhere....I am running 10-10-1 on Alex's advice, and I must say I love the handling, though I'm not experienced in many different weights, but with this setup, I find it pulls nicely thru the corners, and can be induced to slide (very predictably) with a bit of throttle. Does push hard under braking though, but hey, it's better technique to brake toward the corner, coast around and accelerate out anyway...

I can't fix it all the time,new 0-rings,new oil,...
I'm thinking of doing it only when i'm about to race in a serious race.For practise and just racing friends and ... i prefer something close to the oils i use and something that will saty there for 2-3 months.
What are the characteristics of a diff with grease in it?
How does it act?

Like it has 500wt in it at the most...if you're talking regular diff grease and you pack plenty in there, like they give you in RTR diffs...As for the action, grease in the center will make it almost like front wheel drive, grease in the front will make it push thru the corners, dramatic understeer...grease in the back prob won't make a huge amount of difference...someone correct me if I am wrong...

If that's the way it should work,then maybe by using different grease weight i "can" make it work...!

As far as I know, there's only two weights, but again I could be wrong...normal, and locked, which is like 100,000wt silicone...if you want variable action, it's gotta be silicone, buddy.

You can get grease with various weights. Kyosho makes 1000,3000, 5000, 15000 and 30000 differential grease. One of the fastest guys at the track I drive at, uses grease instead of silicone oil because his diff's can't keep the oil inside either.

Well, you live and learn, thanks engrose...

I was just lucky here, because we talked about it yesterday at the track

The kyosho is pure grease?NOT lequit??
And how do you use it?I fill the diff full?

Find where your grease is going man.....I heard a guy saying his prospec won't hold the oil for more then 2 days...said NO diff does....I didn't think th esame so I tore mine down that night I had plenty of oil.....but when I offered to tear his down he wasn't going to let me....I then asked a friend who claimed the same thing about his XB8 (same as my buggy).....come to find out he didn't put these little O rings behind the bevel gears in....it looks tight enough to hold oi lbut it's not....point being they should hold oil, they are designed to.....if they are not then you are missing parts or not reassembling them correctly......try using some sealant around the cup against the ring gear and pack your O-rings in w/ grease....actually I use vasoline there.....neither will affect or be affected by the oil in the cup......

That's good info.Thanks!
I do put it together OK,but i was looking for something that is easier to work with also.
So kyoshos grease is my choise from now on.At least until i give it a try and see how it goes!

why dont 1/8 have limited slip diffs?

There is something similar to a limited slip differential. Its called a TORSEN diff. It uses a unique gear arrangment that forces it to always transmit power to the most difficult to spin side of the diff. This can be good in smooth med-high traction surfaces, allowing your buggy to get maximum grip. It is not good however in rough or low traction conditons because this causes the diff to frequently switch back and forth which side is getting the power. This can cause erratic handling similar to bump steer, especially if the diff is located in the front or rear position.

i think tamiya might also make different "watt" greases

Like plaidfish said these diffs are designed to hold oil unless you don't have it together right. This is the first time I'm hearing of this problem but when you close the diff there really isn't that much room inside them just whatever space is imbetween the gears. When you take it apart it should be about half full of oil or maybe a little less.

If you use 1000 weight grease and 1000 weight oil I really don't see why the grease wouldn't find its way out either. Grease does tend to stick to whatever it contacts but whatever you have in there does get turned up quite a bit. If you just pack your diff with grease other than weights that are close to the oil your running now chances are its just going to be way to heavy and pretty much lock the diff.

That's true.I don't know whether it's liquit or not?
And i think the way these oils work is because they are too sticky and hold(lock) the diff.So if you use a sticky grease then it's about the same but not lequit.Maybe i'm wrong though.

Glad you enjoy the setup Foxy and that is exactly the way I drive too.

If your diffs are leaking this badly I suggest you get some silicone sealant and put a thin bead around the top of the case before fitting the crown/spur gear. Diffs should not leak and if they do then what would be the point of all the alternative weight oils? Plus as grease gets hotter it to starts to liquify and then too would leak out. Now, I strongly think that either the outdrive shafts are worn down as when constructing the diffs many people overlook the need to lubricate them before you slide them into the case/crown/spur, this wears away the O-ring seal and so allows the diff to leak.

In conclusion:

1: Lubricate the outdrive shafts.

2: Lubricate the O-rings before fiting them into the diff.

3: Try the silicone sealant between case and crown/spur gears.

Pennzoil white industrial grease.

Well silicon oil is more of a liquid. Grease is well... grease. Silicon oil in your diffs will give you the most consiatant performance and even if you switched to grease to stop leaking I still don't see why it wont work its way out like the oil is anyway. Just follow what Alex said and if you still have leaks well than your doing something wrong.