I have a Q Bert table top arcade and of course it has a broken battery cover and has been taped with scotch and masking tape, I can get the scotch tape off with the heavy duty cleaner that I have, but the masking tape is another story that stuff has like fused to the case, I can't scrub it too much because I will scratch the housing because it's riggid, can anyone help me or reccomend any cleaner?

It is also missing a battery spring, I want to solder another one on but I want to know if there are any precautions or ways to guarantee a solid connection and that it won't fall off in the future.