Guys:

On the early 140, 91 models, the cluster are the analogue version rather than the digital display.

The VDO analogue cluster ised on 91 140 were having problems with the mother board requiring replacement. A Mercedes bullitten can be found on this. In the early days, MB offers just the board for dale. However now they offer the entire cluster only. The problem is the exact description, lights flushes like chrismas trees....

Search the site for 140 cluster and you will read. Its a well known problem. A bullitten can be found if you look hard enough.

Considering the similarities on the SL cluster with the S-Class, I won't be surprise the same problem exist on the 91 SL class too.

I know someone in the states offer re-built of your mother board. However for a proce of something like 500 USD. Someone tried it, and it was fixed. look in the board and u will see.