The purple wire nuts have performed poorly in tests. To solve the problem without running new wire in the walls, it is a good idea to splice Copper onto the Aluminum so future devices can all be standard CU only. It is best to use splices that do not have the Aluminum touching the Copper. For a few splices use small split bolts with a Cu/Al seperator plate and with Deox. For lots of splices use the COPLAM system: crimps(Cu in one end, Al in the other)with a special crimp tool. Houses with Aluminum #12, #10 NM are many times more likely to have a major electrical fire. Talk to your fire dept!