Both sets of opto's can be cleaned without taking apart the assembly, the top ones are easy, you just look down and you can see them, the other ones are on the bottom of the elevator, you need a q-tip, make sure the arm is in a position where it is not inside the u shaped opto, reach in with the q-tip and clean.

Elevator hold is the top one, elevator index is the bottom, there is also a connector plugged into the bottom one, I had a wire loose on mine, changed the connector, worked perfect again.

The top will take no time with a q tip and windex.

I had similar issues with my Demo man. I took the opto PCB out and pretty much replaced everything. It's relatively cheap to shotgun everything on those opto boards, I say it's worth it. Its been almost two years and it hasn't had a single issue since. I even made a video about it.