This has been discussed to death in various forums but I'm looking for a fresh look at the problem. I have a 1998 and I do question the current findings.
If the bearing was underrated, then all IMS bearings would fail at roughly the same point but they don't. The figures I have seen are 1% of the older cars and 8% of the newer ones. However some cars do +100K miles and no problem. I don't believe that that IMS bearing is underrated. It is highly loaded but within spec. It could have been designed better, however, its not the problem.
There has to be some other factor causing the failure.
Here are a few that I'm thinking of
1 Could a low oil level reduce the oil to the bearing
2 Could it be either high or low RPM be a factor, ie slow town driving or many track days
3 As time has gone on, the zinc, (high pressure lubricant) in oils has been reduced to save the catalytic converters. Maybe other suppliers of oils could have a lower zinc contents. In my vintage race bike, I went through rockers quite regularly till I swapped to a high Zinc oil. Problem gone.
4 were the cars were driven in the odd high temperature days and the weight oil was therefore below the recommended value.
5 Oil does break down over time and changes its viscosity. Were the oil change intervals extended?
6 were the cars standing for long periods of time ? Oil dripped down thus when started the bearings were dry.
Keen to hear other peoples opinions.
Some reading
https://www.timken.com/pdf/5892_Bearing%20Damage%20Analysis%20Brochure.pdf
Spent years chasing 2 stroke seizes till I read this article.
http://www.marshland.co.nz/ftp/Files/topend_rebuild6.pdf
Basically all seizes are oil failures.
Cheers Wallace