Have the 4 Stroke with the Stage III gearbox. Would love to be able to get the cover off to apply lithium grease to the gears. The problem is that I can't turn the 7 screws to get the cover off. They are super tight & no screwdriver I have can even begin to turn the screws. Any suggestions short of TNT to get the cover off? Would I be able to replace these screws with 10mm bolts or will the screws come off easier next time?

Plus...got some 85W-145 gear oil. Several have said lithium grease works best...but others have said gear oil's not good. Any suggestions?