Usually the trimmer Gearbox can be split real easy, cleaned, get all the twine thats wrapped around the shaft, inspected, relubed, and assembled. Very simple and straight foward, just note how you disassembled it. Same goes for the shaft. Don't froget the lock screw that locks the head to the shaft. Straight or curved all the same on Ryobi manufactured trimmers. Done mine several times over the years

ptgr: Usually use light grade Moly grease for this purpose. It resists hardening after extended hours use and heat cycles.