I would be happy if my E32 750 11/88 would have a filter, unfortunately that filter was introduced later, have to clean the aircon/heater system every year, here the official information.
Models: all except E30
All vehicles produced 09/1991 or later (except the E30) are equipped 100% with the microfilter.
In addition all E31 vehicles have been equipped 100% with 2 microfilters since their start of production.
Vehicles with the microfilter are supposed to have a red "Maintenance Reminder" decal in the glove compartment.
However, on vehicles produced during 09/1991 - 05/1992, many of the labels were inadvertantly left off. These vehicles are, however, equipped with a microfilter.
Some vehicles produced prior to 09/1991 may be equipped with a microfilter,and can be positively identified by the presence of the "Maintenance Reminder" decal in the glove compartment.