Went out on this beautiful New England morning to change the differential fluid on my 98, only to discover that BOTH plugs (fill and drain) are sufficiently rusted that there's no chance a 14mm hex socket is going to fit in there.

Obviously the first thing to do is to order new plugs. Then, once those are in hand, what's the best way to proceed? Lots of PB Blaster until I get a good tight fit? My fear is that I'll find them sufficiently deteriorated that I won't be able to get them out.

Is it worth trying a 13mm socket or is there too much risk of rounding it out?

Any advice appreciated.

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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