Mine is split vertically along the venturi. It wasn't evident until the venturi was removed, then a visible gap can be seen on the inside.
Cub. The smallest tank I can find is a 1 oz from Tower, but the Mecoa .3 oz. may work so will check it out. A .020 on 1 oz. would probably run 30-minutes plus! Oddly, I had considered the repair you mention (kevlar thread/epoxy) when the crack was discovered, as I've used that technique on other items. Thanx for confirming it.
Eddie-its one of the flaws with the Cox TD design setup-to avoid the entire NVA rotating you need it done up good and tight-and that's only a small snid away from splitting it. Obviously either split will let air in where you don't want it-and at best they become impossible to needle or won't run at all! If you have the front collet ring done up too tight the plastic housing will either split along the crankshaft axis or distort at the rear where it seals against the crankcase front-once again you can't win! The problem is the plastic is pretty much impervious to any form of glue-even epoxy doesn't grip well, so you can't just glue over the crack. I suppose-in theory at least-you could ultrasonically weld an axial split-but how many modellers have access to that sort of equipment? And for the daring-you could try melting the crack together with the tip of a soldering iron-but there's not a lot of space to get at it, nor a lot of wall thickness. The venturi spigot can be done-as I've mentioned-but its awfully fiddly to do-and you have to make a very neat wrap, cover it with epoxy, without getting it anywhere else-and still ensure no airleaks! A $9 replacement from Mecoa saves a lot of aggravation. By the way I've just checked the Ex Model Engines and Cox International websites-and they both are listing only the metal TD 020 carb housing-so I guess they have run out of the original plastic bits. I also note that Mecoa are doing them in both red and black in all the TD sizes-including the 09 and 15!-which should give rise to a bit of head scratching in the future as I'm sure Cox never did the TD 020 in black, and never did the TD 09 and 15 in red........
On the issue of tanks, check out the Cox International site-they have some suitable metal tanks which would work (they look to my eye to be the same as the old 'Perfect' brand rectanks). One largely unexploited source-available to anyone who keeps their eyes on the footpath......sorry-for you US types....the sidewalk....is the caps off 'yuppy' water bottles and energy drink bottles-the clear cylindrical cap bit that covers the valve part you actually drink from. I guess these are polypropylene-and thousands must be discarded every day. All you need is access to a lathe to make a closure-ideally with a flange quite a bit wider than the open end of the cap, so you can mount it. You have a choice of making it a 'snap' fit in the cap (you'll need to machine a slight groove for the projecting ring on the inside of the cap to fit into) or you can hold the whole thing together with a single central screw through the centre of the cap into the 'base' piece you've just turned up. I use delrin for the closures, but there's no reason you couldn't use aluminium.
A quick scrabble in my odds'n sods bin throws up at least 3 sizes: 20mmID x 16mm deep giving a volume of 5cc, 22mm ID x 20mm deep giving 7.6cc, and 29mm ID x 20mm deep giving 13.2cc or in your money-about 1/5 oz, 1/4 oz and 1/2oz.....and I wouldn't be at all surprised to find other sizes out there. The largest one I mentioned would probably meet your needs.......
So for a little bit of work you can have some very cheap tanks covering a range of uses. And the principle can be extended-women's hair colouring kits (at least the ones my wife uses!) have several useful containers and caps that can be easily adapted.