All radio systems can have some frequency drift. Its probably a good idea to send in the TX's with modules and all the RX's to have them all checked.

Better to pay the bench fees than have a plane go out of control. (though this will be a rather hefty fee checking several RX's and multiple TX's...)

I recently sent in a 7-UAP (via Radio South because its LONG out of warantee, and I like Radio South.) for checkup and repair of 3 broken switches. Well worth the cost to get rid of the glitching that was starting to show up. Appx 17 yr old radio and going strong. Futaba makes good stuff.