I think the rod bearing would go first. I've heard plenty of spun rod bearing stories, but never a spun main bearing story.

FWIW...My 944 has a spun rod bearing. I bought it from a kid who ran it low on oil. The oil pump starved and the #2 rod bearing spun. The mains had not spun...yet. I only pulled the rod caps so far, but the mains appear ok.

I think they will both be damaged, but it seems that the rod bearings always fail first. At that point most people stop driving the car and get it fixed. Thus the main bearing do not actually fail, unless you continue to drive the car.

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1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5