When cleaning my 870, I've found G96 Gun Treatment to be good stuff for squirting into the trigger housing to clean, lube and protect. Leaves a thin film. Especially when I don't feel like removing the side saddle to remove the housing. I use Gun Scrubber to clean things out good, then blow it out with canned air, then use the G96. The G96 is not gummy, and the new Synthetic Safe Gunscrubber seems to leave less white deposit--not that it's a concern. I'd never remove a staked rail (shell holder).
If my SIG trigger pulls seem a little rough, I squirt some G96 in there and things improve significantly--and it lasts quite a while.