Just repeating what I've read elsewhere (from knowledgeable sources though):
Its not that the oil pump is getting weak, its that the main bearing clearances are getting a little loose, reducing oil pressure.
You could use a 'turbo' oil pump to make up some difference. Ted at Enginebuilder sells a turbo-spec oil pump (not the same p/n, but equivalent, since the true turbo pump is both $$$ and getting hard to get) FWIW.
Or thicker oil, and just keep drivin'...
Sure its not the infamous timing chain slap?
