Preheat and apply force from the bottom rather than from the side (this way you're less likely to bend the PCB). For example, you can just stick a long knife under the HS along the contacts and then twist the handle.
So much this!
I've recently seen a board go from mem CBB at -10 (on three different kits) to easy full pot (on two of the same kits) just after digging an impact-reset-button-sized amount of dirt from what looked like clean RAM slots at first.