This happened to me shortly after i put a vit lump in,
The engine looked a good'un but sadly something went wrong and i suffered with the oil pressure light flickering away. I swapped the pump for a used one and this cured the issue but very breifly, when i had drained the new and fresh oil id put in there was a heavy metallic shimmer to it.
i just accepted it was doing some damage and knowing that i would be replacing the engine, i thrashed the ass off it daily trying to kill it and ran it on random oils i had in the workshop, even some old used stuff and accidentally some used brake fluid went in there aswell.
Never did die suprisingly, used it like that for months, smoked and rattled,knocked alot when cold tho but still went like stink

.