Here a link to optional springs:
http://www.varishock.com/c-68-12-coil-springs.aspx
If you can get some sort of travel indicator on the shock shaft that won't damage the seal or shock body that would help determine if the shock is bottoming and causing seal failure. Small tight fitting O-rings work well if you can get them on, clay, tinfoil, or? When you have the shocks rebuilt you could ask about having them installed. I have them on my track bikes front forks and they are very handy for dialing in compression settings and maximising travel.