I think your car runs W7DC's. I suppose you could try W8DC's (Not the WRxDC's - R= resistor) as they are a little hotter I believe. A little smoke could be valve seals, and unless the plugs are fouling I would just run it as is until you do the seals.
I have heard of folks pulling the solenoid and cleaning/lubing and reinstalling. One of the guys at wourk did that three times on his SLC before springing for a fresh Bosch rebuilt. Worth a try.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.