I'd try a couple of things. I'd suggest buying some new paint. Perhaps buy one jar and try it out on a scrap model. I suspect the age of the paint, especially metallic, has a lot to do with your issue. Also, those metalizers shouldn't need thinned so again probably the age of the paints is the main issue. Also make sure you have a vapor trap attached to your airbrush hose. If there's a lot of humidity where you live that can cause issues too. I've not had much success with MM Metalizers. I prefer Alclad as they are quick drying easier to apply and very easy to mask. The metalizers can be difficult to mask if your planning on doing multipule panels as the paint will tend to peel off when you remove the tape. Although Testors has a Metalizer sealer that you're supposed to use with it too. Other folks may have had better success.
I hope this helps.
Here's a model I did using the Alclad NMF
Neil
P.S. I love you're avitar!