The B230FT can last to ~300K miles (maybe more?) IF well maintained but most of the older ones (pre-'93s) developed piston knock from excessive wall taper, piston to wall clearance even though they often seem to last a while knocking almost as loud as an old diesel engine. Mine was knocking louder than I liked nearing 200K miles so I replaced it with a newer type (940 engine) which has piston cooling, etc.
The water cooled turbos like yours can last well over 200K miles if oil is changed often and synthetic oil would be better yet.
One of the biggest problems I see which happens to those older turbo engines is that with higher mileage they often burn more oil and their owner doesn't realize it, doesn't check the oil level as often as he/she should and thus runs it very low on oil which does wears it out prematurely. It's not unusual for a B230FT with over 100K miles to burn 1 qt in 1000 miles and that in itself isn't that much of a problem (adding the occasional qt vs an overhaul) as long as you know it's burning that much and add as often as necessary. I've seen several come in for various repairs, maintenance and notice the engine knocking louder than usual or see the oil light flickering only to discover that it'll be 4 qts low (out of 4.5 qts total) so it's obvious then that that engines life has been seriously shortened.