The switches are not the biggest problem. More so, the o rings failing on the cylinders which tend to happen only when someone is wearing their favorite shirt. There are 12 cylinders in total and some are a total b*stard to get to. It's a 15-20 hour job. The gearbox problem you describe sounds like classic conductor plate / round plug tcm cleaning job.
I had a 300SL-24 with a 5 speed manual and even though it was in horrible shape, it was a delight to drive. I'd buy another. The beauty of the R107 is its simplicity. Anybody can fix one and because they were made for such a long time, and were so popular, support for them is still plenty strong.