My 91 745 turbo suddenly start doing the horrible noise when turned on first thing in the cold morning (so much colder than a normal year here in the Midwest almost all my cars and trucks are having a hard time). I thought that the motor is shot. Before I picked up the phone and ordered a new one, I took it out (thanks to the FAQ archive) to take a look. The cage looks fine the motor axle has minimum play . I do see old water marks (rust) in the plastic “cup” the motor sits in and on the bottom of the motor where the bearing is. I clamped it on a vise upside down and soaked the center bearing area with PB bluster followed by WD40, followed by light engine oil while spinning the cage for over 5 minutes. After the treatment, the motor spins very smoothly (also sprayed a lot of WD 40 into the motor from the holes on the back in hope of getting some into the front bearing). Put everything back together and now I have my heat back, as smooth as ever).
To prevent this from happening again in the future rainy day driving, I decided not to install the plastic with the cup thing. If you really want to have it original, I guess that you can drill a ¼ inch hole in the center. I hope this can be added to the FAQ archive. Following the statement below:

“The reason the original fan failed became quite apparent in today's rain. Water showed up around the new fan. Apparently the 740 has a tendency to leak on the passenger's side with the water ending up in the plastic basin that the fan sets in. [Note: See Volvo TSB for a fix for this problem.]”