The ceramic inside the resistor can sometimes get damaged. I've heard this sort of thing doesn't always show up using and ohm test as John described. Can't say for sure that I know this to be true.
An MB tech I know told me that they often times are damaged on removal if you do not pull them straight off. If you get into a back & forth or circular type motion, you could damage the ceramic interior portion of the resistor.
Some here have suggested using dielectric grease to lube the connection in order to facilitate removal the next time around. You might try doing a search on dielectric.