[thstone]

With about 225,000 Boxsters/Cayman's sold, my guess is that the IMS failure rate is somewhere around ~2%.

This is based on about 2,000 L&N IMS replacements sold to date (all assumed to be out of warranty repairs) and probably an equal number of warranty engine replacements for IMS failure.

Of course, not all L&N IMS replacements were failures, some were preventative replacements while replacing the clutch, but I am making an assumption that for every preventiative IMS replacement there is someone who simply replaced their IMS failed engine with a stock donor engine without any IMS upgrade.

Also, I haven't read any thing that would indicate that higher milage cars suffer a higher rate of IMS failures - if anything, the anectdotal postings indicate the opposite. This implies that failures are essentially random and that mileage is not a key factor (they will be evenly distributed in mileage). Thus, I am able to assume an equal number of failures occurs both under and out of warranty.

Any failure rate larger than 2-3% (for instance a 5% failure rate would be over 11,000 engine failures) just seems too big to ignore. In that case, we'd have owners crawling all over the internet looking for replacement engines and literally thousands and thousands of Boxsters flooding Craigslist and eBay with blown engines for sale. And I just don't see that, e.g., my search of eBay two days ago only found one Boxster with a IMS blown engine for sale.

Just my own back of the envelope estimates and assumtions. Would welcome to hear from anyone with some other ideas or numbers.