GBB's need plenty of lube and maintanence, more so than AEGs in most cases. Keep the barrels clean, the moving parts free of excess lube and debris.
Always discharge your batteries, and make sure to fire a shot or two on semi after you get done using the AEG (to decompress the spring). Keep magazines clean too.
Basically, you have to disassemble, clean, lube, and reassemble everything after you have used it for a while.
You need high viscosity lube (grease) for AEG gears, you need a lighter kind of lube for moving parts outside of the gearbox (the hopup).
I haven't heard anyhting about slamming the action on GBB's. I suppose it causes additional fatigue, but GBBs are always getting slammed around.