My car is a 1989, there are 2 choices for motor mounts for my car, how do I tell which month my car was built?

(One motor mount is for 10/1989 and on the other for 9/1989 and below)

Thank You,
-Rahul

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2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)