Did you try the dealer?
Part Number 6062000096 Part Name BLOCK HEATER MSRP $142.00

Picture here. It doesn't seem to have the ring you are looking for.

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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss