I had all symptoms of buil up, and was using just a single product with amodimethicone (Fresh Curls - Redken). When I stopped using, I improved. Then I went back to using, and again I had build up. But, I have to agree with you, I wasn't using a "matching".
About mineral oil... wow!...
After reading your post, I have been searching on it and I was excited about what I read. I had not considered using mineral oil, for it be derived from petroleum. However, from what I read it looks like it may be the sealant I need.
Has Mineral Oil Gotten A Bad Rap?
Hairloss and Topical Coconut Oil Pre-Wash-The Ultimate Hair Conditioner
Here in Brazil it is summer, and this year is particularly dry. It is difficult to keep moisture, DC and PT. So, I'm going to try the mineral oil as a sealant. I hope it's my HG too!... (: