I am using an rpg250 spool gun, purchased from HTP, but i think it is a standard. lincoln makes one like it. after 2 years of use, it has begun to have intermintant arc stability on aluminum. i sent it back for repair , and they ran my spool of .030 super glaze 4043 through with no problem, however, upon its return it exhibits the same problem. i use an HTP200 mig machine which never has problems, but the spool gun is killing me. the wire feed is on the gun, and has a very limited useful range. 10 is often too slow and 20 is too fast on a 100 point dial. but there is no consistancy. i get dialed in and run a perfect bead, then the next is fast, slow, dropping out, spattering, leaving a very rippled bead. often, it is dull grey in color. then it will be fine for a bit. i do notice a rhythm to it, every 5-6 dimes, it will go bad. any clue would be helpful. i have considered getting a different gun, but do not how to integrate to my welder.