Keep in mind the availability of parts when buying a used/new Springer. Crosman parts are cheap and readily available. Gamo or Umarex not so much.
I haven't had success with my B3 project yet, I'll tackle the project again soon.So a little about my B3-4 of F model, the cocking rod was so hard to pull that it bent a little, the problem is the screws holding the stock on by the pivot area are too long. I used a bar clamp in place of my usual spring compressor, inside the compression tube was the usually greasy gunk, which I cleaned out, the piston seal is hard and appears to be undersized it also looks a lot like a clear plastic.I lubed with some moly, probably too much, I didn't get the trigger assembled correctly so the rifle doesn't cock. It has been sitting in my closet for a month. Other projects have had my attention, but I will get back into the B3 project again. And when I do it's getting more than a lube tune.