Should I change the plugs? It is 4 years old with 65000 miles. It runs very smoothly. I don't want to do anything stupid to mess up a perfectly working machine. Is it difficult to replace? The space around the engine V8 is very tight. Do you guys have any tips?

Car Nut
1999 E430 Sport

The recommendation on a 99 is 100,000 miles or 4 years, I'd replace them.
"Have a good selection of tools" is about the only recommendation I can tink of.

Gilly

I just had the plugs replaced on my 1999 E320 with 55,000km (34,000 miles). I thought it was running smooth before the plugs were changed. At first I didn't think it would make a difference but it is actually running smoother now.

I'm following the manuals maintenance schedule for service time intervals regardless of the number of miles I put on it.

3 star

I actually thought access was good when I did them on my '99 E430. I took off each coil unit from the valve covers. I took out the air cleaner housing. The only tight spot was the left rear set of plugs, but a 4" extension is just right and makes short work of that set. To pry off the boots at the plugs I used a peg board hook. I bent the two prongs that fit into the peg board for a snug fit on the boot and slid a length of 1/8" pipe over the opposite end as a lever. Worked like a charm.