Well, I fitted the new ignition leads to my 1994 R129 SL500 today. It now has new engine wiring harness, distributor caps & rotors, ignition leads, and plugs. The regular misfire is gone - Hurrah! HOWEVER... It still runs roughly, and misses, splutters and holds back under throttle - quite badly; it's really not realistically driveable, though it could limp a few miles to be fixed. Additionally, the thermostat appears to have come out in sympathy; it took AGES to warm up, while being driven, not at idle, and never did reach the 80 degrees on the gauge that it should. Even when it did reach something like running temperature, it didn't run much better. Could the two problems be linked? Anything fairly simple I could check? And there's more... The kickdown (four-speed 'box) doesn't. I presume this is likely to be linkage adjustment? It changes down normally using the stick, and changes automatically on part-throttle, but on full throttle going up a fairly steep hill it just sat there, throttle wide open, farting along at about 45 mph with the speed only increasing very gradually. AAAARGH! Just b****y AAAARGH!!!