In my 91 300D, somehow I managed to lose the plug that was in the hole where the headlight washer pump used to be (removed many years ago, prior to my ownership). I thought I might just permanently seal it with gutter sealant or JB Weld. Or is that a bad idea? If I need to get a rubber plug, where might I source something like that? I assume it's long since NLA from dealer. I can obviously just buy an assortment of rubber plugs and find one that fits...but seems kinda trial and errorish.

I talked to the folks at JB Weld....they think the best product of theirs to use would be the plastic weld putty.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Used two flat washers, two rubber washers, a screw and a nyloc nut. Screw, metal washer, rubber washer from the top. Rubber washer, metal washer and nyloc nut from the bottom inside the tank. All hardware stainless, works like a charm.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Not an expert on 124's, but MB used this plug for a LONG time. 0009973320. Seems like I had to drill my 123 out to 10mm to use it.

Actually, it looks like the plug is still available...maybe that's my best bet.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I’m pretty sure I just bought a reservoir pump for this same reason. I can’t seeem to find the part numbers but there were grommets and plugs depending upon if it was for a pump or to plug a hole. I used the typical EPCs and then bought at pelican.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)