I have been running a replacement Blackstone in my 87 745T since 1999.
That was around 175K miles and I have 356K on the car right now with no leaks or cooling problems.
Originally I went with the conventional wisdom that the all metal three row were better than factory. With in 24 hours of installing the all metal the radiator failed catastrophically. It blew out and I'm not exaggerating, all four corners. Lucky for me I was less than 2 miles away from the dealer and it was all down hill to the dealership. $400 and less than 45 minutes later I was pulling out of the lot. Yep, I installed the new radiator right in the parking lot. You should have seen the faces at the radiator shop that installed it when I returned the metal one for a refund.

The Blackstones are good for 8 to 10 years before problems start to occur.
After 10 years you ned to start keeping a close eye on the radiator especially the end tanks and plastic necks where the hoses attach.