Remember that time on the way to The Vintage in Asheville in 2018 when my wiper motor died in Winchester VA and I drove 81 South in pouring rain? Then at the show in Hot Springs, Billy Revis & Rob Seigel & I swapped out the wiper motor for one from Billy's M6? That was awesome!
What had happened was the original motor's internals got wet and shorted the motor. When I tilted the water logged motor rusty water poured out the weep hole. I know people cringe with coupes and rain but when traveling, rain happens.
So today I modified a 2002 wiper motor cover and installed it. The bolt pattern on the E9 is opposite of a 2002. Luckily on the back of the cover are mold marks that just happen to line up with the E9 bolt pattern. So I drilled those out, then had to cut the far end off as the E9 motor is also longer. I used the original wiper motor to test fit & modify the cover until it fit.
A little trick I use for messing with wiper motors is to tape the wipers to the windshield as parked & tape the linkage pivot on at the motor so nothing moves when the short pivot arm is pried from the splined shaft. The motor mount bracket has a small flange on the bottom so I had to further modify the cover to fit.
Then reinstalled the wiper motor. Put the linkage back on the splined shaft. Untaped everything and as a precaution raised tilted the wipers up tested. Everything works and the wipers parked right where they were before.
Hope this helps to mitigate water getting into the motor or at least slow the process down.