I own an OM M1991A1 as well. I would suggest that if the pistol has not been fired much, put a few hundred rounds through it before having any work done. My own pistol has a pretty decent trigger and I have done nothing to it other than add a Colt short steel trigger from a series 70 pistol and a Colt nylon arched mainspring housing.
If it still is not to your liking after some shooting, it would take it to a good gunsmith and have him lightly polish up the lock work. The standard Colt parts are quite good so I would not replace them.