The signs of failure are usually a bottom-end knocking.Hi mmm, what are the "signs" you mention for the rod bearing failure?
The only way to check for wear (without stripping) is to take regular oil samples and get them tested at somewhere like Blackstone labs for elevated copper/lead levels (from bearing wear). But you need a few consecutive readings over time to see the trend, so a one-off sample may not tell you much.
Mine was fine for 140,000 miles, of more than prescribed oil servicing, but it went from quiet to knocking between a lap of the Nurburgring and starting up again after filling up with petrol for my next lap. I could probably carried on driving it, but I wanted to get it to a garage before I was stranded with potentially a much bigger repair bill for a full rebuild, rather than just the bottom end.
The alternative is to do a preventative bearing shell change every 50-60000 miles.



