I removed my 1994 R1100Rs. Gas tank to bleed brakes. Now the tank will not slide forward enough to put the gas tank Allen bolt in to the hole . It is about 1/4 “ too far away from the front of the bike .too far back. It used to fit , I can not see

Putting a small amount of grease on all parts of the tank that touch the rubber mounts helps. When the rubber becomes dry it has a lot of friction against the steel surface. At 26 years old they're probably pretty dry and cracked. The grease helps to keep from pushing them out of their position when reinstalling the tank. Good luck!

Check the rubber bummer in front of the tank. Look and make sure that it's on the mounting plate. If it's not correctly on it may be causing the miss alignment.