I actually did have a John Deere concern for a while a few months ago. The seat on my 620 suddenly seemed to tilt down toward the front of the tractor, so I was thinking the shock absorber must have gotten "sprung" or some such thing and would need to be replaced. I ignored it for a while, intending to look into it once the weather got warmer. But I eventually noticed (duh!) that the seat suspension arms had somehow popped free from the pins that support them on the front side of the battery box, and just needed to be set back in place. Easy fix. I'm not sure how they came off to begin with, but I suspect it happened when I was using the rear blade to level some ground where I'd recently burned out some big stumps... the blade caught a root and stopped forward motion of the tractor, causing (a) the front end to suddenly rise, (b) me to grab the clutch lever while cursing my stupidity, and (c) the front end to drop back down. Must have been enough of a jolt to bounce the ends of those suspension arms off their posts.
Anyway, all's well that ends well, and the 620 is back to normal and I'm a bit wiser about use of that blade.
Saint Paris, Ohio