Boarder Line Low Oil Pressure

My buddy with his BBC with twin turbos, last time we were at the races, he lost oil pressure.
Super low, duel oil pressure gauges reading the same.
Expecting the worst, last weekend started to tear into the engine, what he found was the VR-1 had totally broke down in 300 miles.
It was thinner than water when it was drained, no viscosity at all.
Fresh oil change, using the same weight VR-1, oil pressure is back to normal.
Only thing we can think of, is the heat from the turbos, basically cooked the oil.