Boxster Engine Failures - Some Clarity Please

[Seadweller]

I know this has been beaten to death a thousand times, and I've done a lot of reading both before and after buying my '98 (which was delivered new in December of '97), but I'm not clear on what modes of failure affect specific year models. Any input on the below would be greatly appreciated:

1. The prior owner had the IMS replaced with an LN Engineering version, and at the same time, the RMS replaced with the updated version, at around 27K miles. The car currently has around 36K, so I'm assuming these two major items won't be an issue near-term.

2. I've read about "D-Chunk," but my reading indicates that it was most prevalent in cars manufactured over a certain period for the '99 model year. Does this mean my '98 is less likely to experience this failure?

I know there are a dozen more, but most don't cause catastrophic failure, with the exception of the rod bolt issue and chain tensioner issue.

Is my understanding of the above correct?

Oh, and one other question...Does it make sense to upgrade the tensioners to the updated version as a preemptive measure?

Thanks!