I had water that landed on and caused corrosion on the liftgate motor contacts. They stopped lifting. The mooroof drains were not fitted correctly during a cassette change out and water ran down the headliner into the well were the contacts and tailights were. I do think the dealer said that drained the lenses.

Maybe your issue.

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Arrived - '11 35d Alpine White/Black, Sport w/Adaptive Drive, 214's, Tech, Prem, Ipod/Sirius, R Climate, Probably no First Aid Kit
'01 Suburban "Shrek" 130K miles and still strong.
'01 Volvo S40 1.8T - Inherited by youngest daughter
'06 Acura TL MBP Navi Camel - Inherited by eldest daughter
GONE - '09 35d Alpine White/Black Sport, Tech, Prem, Ipod, R Climate, No First Aid Kit