I too had the same problem with my 93 850. The belt in the front is too short. I bought a Mamas and Papas travel system and the seat fitted in the back fine but not the front.
Now have a MaxiCosi Priory XP (as my daughter is too big for the other one now) which fits fine. However, before I bought it I checked out the Which? guide to car seats. The results shocked me. I could not believe how many of the seats are unsafe and that compulsory testing is limited. Apparently they don't even have to do side impact tests.
If anyone would like the report please e-mail me and I'll see if I can attach a copy by return.
Regards
Andy
andy.donnelly@ctcplc.com