Jerry V,
Not being a ML shooter, I didn't realize that nipples were so consumable. So, finding a regular supply of them is important or purchasing them by the dozen? Again, I have no experience with ML's but a sleeve or entire nipple made from one of the high nickel content SS's used in high temp aerospace applications like Hastaloy, Waspaloy, Inconel, etc might be a near permanent solution. Small bits of these alloys can usually be found at many SoCal aerospace scrapyards.