I'll second the advice to check the connections at the switch. I had loose connections on my '88 240. I reached up and pushed them back on. All was fine. I don'r know if it will help but I recently replaced the 4th gear switch which is on the opposite side of the tranny from the back-up switch and as hard to reach. I found that a 7/8" deep socket would fit the switch. This socket was made to remove the oxygen sensor from tight places. It could accept a 3/8" ratchet or, since it had a hex head at the same end, you could use a 1" open end wrench on it. I was able to remove the switch without having to lower the tranny. It was about a 10 minute job. If you remove the backup switch, be sure to clean the gunk away from it so none will get into the tranny.