Pulled the instrument cluster yesterday.
 

The temperature readout hasn't been working for a long time so I decided to see what could be done. This is on a 95 SL500, so don't know if it is specific to all 129's. Pull the lower bolster off,,, 5 screws. I then reached up to push from behind, but there was NO WAY that I had the muscle to break it loose. I then got a pry bar I had laying around,,, wrapped the end in layers of rags, and proceeded to pry very gently on the left end of the cluster. There is a round cross brace at the bottom of the dash that makes a good backstop to pry off of. Finally it started coming out until I could start wiggling it a bit and do the coat hanger trick on the right side. I had the left side out far enough to see the ridges to know where you had to hook the coat hanger on the right side. Once out, there are 4 simple push on plugs that you just pull off. Next time should be a LOT easier. BTW, I switched a bulb around and the temp readout is working now.:D

I have a 96 SL500 with the same problem. I was hoping for an easier answer then pulling the instrument cluster. So I take it that there is no way to get at the plugs from under the dash without taking the cluster off.

Not no way,,, not no how.