Could be the rebound damper o-ring. The older RS Recons and Toras had a problem that sounds similar (I've had a few of them). What happens to those is the damper oil goes past that oring seal and fills up the lowers then the fork really can't compress it has no room. I have those o-rings, I had bought a quantity when they were pennies for the Toras. I'm not sure if they're the same but we could try. It could also be the moco damper tube cracked, another common problem. PM me if you want to schedule time to look at it. I'm not a shop, I do it for fun but have been doing it for a really long time...