[Mart]

Have the same 2.5L block in my 97 boxster, just pulled the IMSB at 80,000km as a preventive maintenance measure, bearing seal was still very much in tact and bearing exhibited little play.
As San mentioned, the first gen 986 came equipped with a double row bearing with a comparatively lower fail rate than the later single row bearings.

As advised by many gurus on site here, best treat them as maintenance items and you should be fine. What prompted me to look at it was oil on the ground. As it turned out, it was the RMS and rubber seals on the auto transmission pump.

Slapped on a LN retrofit IMSB, changed the hardened rubber seals and the AOS at the same time with the transmission box off and she runs like new now.