The rear doors on the 87 190d are only opening easily up to the halfway point. If you shove hard, they open the rest of the way, but with a sickening groan. Im assuming I maybe just need some grease and it would be pretty easy to remedy, but ive never done it before. Any suggestions on brands/application methods? Also, the sunroof opens SLLOWWWLY, maybe it needs some grease as well?