Just to relate some 420 woes.....I have an 87 with 187000 in 8/03. Was burning qt every 500. Smoking on start up. Went to do a valve job found #1 cylinder scored from bad plug. Bought engine from MB salvage yard from same year with 107 miles. Come to find out had recient valve job. Pulled top end off old eng and dropped in new block with new TC, waterpump, motor mounts, etc. Car was reborn and does not use oil between changes and no smoke. More power all around. Was totally worth the changeout. I invested $5k in total project labor included. Have 206 on body and 110 on new powerplant. Where can you buy a car as nice as this classic for that kind of money.....So you work around your problems even if the worst happens...Take the car and evaluate all suggestions. Your enitial investment is less than mine making it worth putting a little money in to fix it.....
Later...
Dave

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Dave Bunker
1987 420SEL, 180k strong Blu & Grey
2004 Road King Custom
Sacramento, CA
tvbunk@comcast.net