Just something to consider. Years ago when I started seeing LA's show up at the field we ran into a few cases where the backplates would get loose and leak air. Basically the plastic would creep (relax) over time and the screws would loosen up and an air leak would develope making for an impossible to tune engine or they wouldnt run at all.
Once the problem was diagnosed the fix was to use some loc-tite on the screws to keep em tight. Minus that Ive never had issues with them.

Funny thing is I never kept loc-tite in my field box until then.

Cheers.