I am trying to replace the plugs on my W210 and after following the great DIYs here, I can get the plug boots off.

However, the plugs are not easily coming out. I've turned them about 5-10 degrees ccw but they feel as tight as ever. I keep checking my wrench to be sure I am turning them ccw!!!

Do people use a squirt of penetrant on these typically to help them along?

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2004 E320 4matic
2000 E320 wagon
-- in the past---
1992 190E 2.3 5-speed! (European Delivery Baby)
2000 ML320
1978 240D - 340k mi