I can't speak for the 40cal. but on the 75B in 9mm the grip screws can't actually touch the magazine, they're behind the magazine break. However if that is the problem then yes, you can use the washers that were on the original grip screws or any other washer that will fit.
If the screws are not the problem, you may need to remove some of the hard plastic backing plate on the inside of the grips. I think I had to do this with mine. If you have to, bolt one side of the grip down leaving other side loose to see what may be causing the problem when inserting the magazine.
If you use too much or the wrong type of thread locker you can apply heat to the screw and it should come out when the locking compound turns back to a liquid.