98-99 are probably the most reliable of the 986 series. Dual row IMS, better chain set, few overheat or oiling problems that later years face. 2-4% IMS failure rate. A garage queen with only 28k is actually at higher risk of failure than one driven daily though. Replacement 2.5 motors are plentiful at dismantlers for $3k or you could drop in a nice 3.4L for more and have Boxster Spyder equivalent performance.
Probably time to sell it to me now for $2k and avoid all that nastiness.