I have seen a number of blower motors stink as they fail. Unfortunately the intake is in an area where it will also pull in oil burning from the exhaust so verify that first.
If it it is the motor, I have never seen it do anything except finally fail. Usually soon after the smell. The motor won't have anything to do with how cold the AC is only the volume. If it is not blowing strong it won't seem as cold.
Bosch Master, ASE Master, L1
33 years MB technician