A lot of good info to digest. You have replaced the springs and one "nylon piece" Valve Guide. I would consider replacing the other two Valve Guides since the other two are perhaps worn. Put one or two drop of valve oil on them and slide them up and down a few times. Since you are still experimenting, stay away from "lapping" your valves until you become more experienced technically. Have your local technician do that. One thing that you may consider, as stated above, is give your horn a "good" bath, which you should do every other month. Take all of the slides out and put LUKE WARM vinegar in them and let it soak for about 20 minutes. This will loosen up some of the gunk that may be there. Then rinse throughly and set them in the tub with the horn. As for the valves, take Liquid Green and spray the valve casings and brush with a valve brush. Rinse throughly and put in the tub to soak. The valves themselves, clean with Liquid Green, then rinse and clean them with liquid dish detergent. Rinse throughly and let dry. Then wipe with a micro cloth. Apply piston valve oil. (Be sure to remove all of your felt pads before doing this) Dry your horn and reassemble and let's see what happens.