If you are talking about the Losi brand Mini shocks that have the cartridge, I have O-rings that fit the cartridge and prevent leaks between the cartridge and shock body:
The only issue is that they seal so well, they make it difficult to bleed and assemble the shocks. So I came up with the idea of drilling the shock bodies for bleeder screws:
The problem with the bleeder screws as shown is that it limits how much you can compress the shocks because they interfere with the piston movement. You need external 1/8" limiters to keep the piston from hitting the bleeder screw. I am planning on trying to drill a set for top-entry bleeder screws (like on the original mini-slider plastic shocks) but haven't had time to do that yet.
If you want some of these O-rings, I'll sell you a dozen if you send me $5 cash and a SASE to return them in. No PayPal on this small a transaction.