Does the key turn in the trunk lock? My last E34 was a Michigan car and only had salt for 8 years. That somehow gathered around the trunk button and worked it's way in there and jammed it as if it was still locked. I sprayed around the button for a few days and would hit the button pretty hard to work more lube in and eventually it popped open. My trunk only had a little surface rust around the License lights.

That 8 years was the end all for poor Nika. When I went to swap tires back to summer ones I couldn't jack it at the jack points. Had to use 2x4s so it wouldn't crush completely. Got another E34 off Ebay and sold Nika making a $20 profit.