There are some lubes out there that would help. I just think finding and fixing the problem is the better way. Lube will only mask the problem and could case other problems. If you plan on being in this hobby for a long time. Use this to learn the right way to fix a problem and it will help you down the road.
If your servo is binding only when both linkages are attached, I wonder if part of the problem is at the servo. Are you having to pull the arm over to the servo output shaft to get it on? If so, maybe a longer arm or a move of the servo is in order.

BTW, the nose wheel dose not have to move much to be effective. Matter of fact, too effective is worse than not enough. Flying on grass is not a problem, but a sensitive nose wheel on a hard surface can be a problem. I set mine in the drive way with the engine off. Just center the rudder and roll it down the drive. then adjust the linkage on the nose till it rolls straight.

david