I pulled plugs and cap to take a look b4 spending money. Cap looks new.
Some plugs look yellow as Gilly said they would.
#1 PLUG= Very yellow
#2 PLUG= A little yellowish
#3 PLUG=Some yellow on one side
#4 PLUG=white
#5 PLUG=Slight yellow
#6 PLUG= tan/brownish
Looks like time for another set of valve stem seals $15.00 bucks.
I will try to take another picture of plugs upload failed.here is the cap

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88 W124 3.0
96 R129 119eng
06 ML350
98 ML320 sold
02 CLK55 amg