C4.1 gearbox to chassis screws coming loose

[southern racer]

Used my C4.1 for the first time last eve and noticed after a couple of heats my gearbox to chassis screws had come loose, all 4. They still do up tight so don't think they are stripped as such. Has anyone else suffered from this?

Any remedies?

Don't think longer screws are an option as would touch the diff? Maybe threadlock might help even with delrin casing?