My Father is still driving his '86 245 with over 400K on the original "skinny rod" B230F. Of course, it is not a turbo, but if you were to believe internet lore the bottom end should have exploded years ago. It still blows 180-185 psi on all four cylinders and pulls hard (for an n/a motor).

The headgaskets in the n/a motors seem to last "forever" provided that the engine is never overheated. I've taken half a dozen B21/B23/B230 motors to over 300K and never had to go inside the engines for any reason.

My guess is that the worst problem you will encounter on a high mileage, sanely driven B230FT is headgasket failure somewhere north of 200K. Now, if you start cranking up the boost and drive your car like a madman, a skinny rod motor will blow up sooner than a fat rod motor, but in a car that is driven reasonably the bottom end should be good for at least half a million miles.