I love my 512. Does yours have a wood or synthetic stock? I'm thinking wood if you say the gun is heavy. If synthetic I may be interested.

The market for 512s is pretty good. It will sell quickly if it's in good shape.

I don't know why you have a problem with the scope mount. Mine is fine with a Bushnell 1.5-4.5 variable. The easy answer is to shorten the stock a bit. This will help with the forward-positioned bolt handle too.

I guess the only way I'd sell it is if you really need the money to buy the next gun.