wiper problem

I have a 1994 Villager with what seems to be a weak or sticky front wiper motor. It only wipes when I put it at its highest setting, otherwise it tries to wipe but isn't strong enough. I took the assembly out and lubricated the joints and bushings but it didn't help. Before I go to replace the whole assembly, is there something else that could be causing this, and if so, how do you fix it?
Thanks.

Check the switch. I found that the electrical contacts were not soo good. Clean and lubricate with electrical contacts oil or change the block.
Hope will help.