Hold on here-- I agree it should be very easy to take off. One thing I have learned is that when I take my FEL off, I always watch the FEL support stand. watch the feet on both sides and see how much it pushes down on the ground. If the pin is stuck on the right side then the feet on right is not pushing up high enough (hence the reason for adding a shim.) After 2 years of on/off, it pretty comes off so easy from use.
is there a possiblity that the FEL stand is bent a little ?
I know I have bent mine up because of the uneven ground trying to get it on. Getting it off is easy. (Just a thought, but you are putting the stand down right?)
Another question, everyone keeps talking about the paint in the holes, does the pin slide easily through the holes when it is off, no binding? Same clearances on both the mount and the FEL?
I do know some times I have to wiggle mine out but not too often.
As for the comment on flat and level another poster made, there is a difference, and mine actually is hard to get on and off when the ground is level. Odd, one would think it would be easier?
The fact that the salesperson took it on and off without issue leads me to believe that there is NO PAINT (unless it was transfer) and you are binding it somehow while trying to take it off.
Also do not file those holes. Those tolarances are there for a reason and too much (I'm sure you didn't go over board) won't be a good thing.
Also, I do not how your concrete is, so I am not making statements about yours, but I have seen very few contractors that can do a level concrete floor, I've got small swimming pool in my basement, so I know from experience and from seeing too many jobs. So there might be a binding issue. I would try adding small shims to the bottom side of the stand on the sticking side while leaving the good pin in.
I doubt that you have damaged anything where the pins have gon through, I have chased mine around the yard the first couple of times trying to reconnect my FEL, and I never dod any damage that wouldn't grow back.