VERY few piggyback shocks are worth their cost. Most do not give you any better function than stock RTR shocks.
Leaking out of the box sucks, but it likely just did not have the cap tightened good enough. I would take it off, remove the cap, top it off with 30k weight shock oil and put it back on. The rs10's ive had the shocks held up as well as any other crawler shocks Ive owned.
I cant recall the MM they are....but if you measure them then you can google the measurement in inches and convert to MM. Just type in google search 4.5 inch to MM (as example) and youll get the MM length and then if you really want new shocks you can search ebay to find ones of similar length. But be prepared for sticker shock. shocks (full set) start around $30 and go up from there.