I've had the exact same problem with my 96 SL1 for the last 4 years.
(Since I bought it, used)
After replacing plugs, plug wires, O2 sensors etc to try and fix the
problem, I stumbled across this.
http://www.magnecor.com/magnecor1/Te...ns/TECHSAT.HTM
I did as they recommended (Buy new plugs and gap them at 0.04 instead of
0.06 and VOILA! The problem is long gone.
The silliest thing imaginable, but it works.