Are these 10-rd mags? Or factory 19? Or the new factory 20? DPMS had a bad batch of factory 19-rd mags a few years ago. They were VERY good about replacing the mags.
That said, have you taken them apart and inspected the insides? There may be an internal defect.
Not sure about long term use of silicone due to the need to keep them clean, but sounds like a good debug tool.