93 400E Thermostat question
 

I think the engine on my 93 400E may be running cold. Even after 20 minutes of driving between 45 -55 degree temperature it barely touches 80C. When I tried to order a thermostat they ask if it is motor# 12-020-771 or 12-020-772. The guy asked me to look in the engine just above the block. When I looked the sticker that his this info is worn out and it is unreadable. Does anyone know which one I am supposed to buy ?? The engine was made in 10/92 - Stuttgart, Germany. Thanks
smk_texas
93 400e , 110K
86 BMW 325e, 147K