In the US, the FCC is concerned with possible "Spurious" signals that the transmitter may produce after swapping crystals. Without testing on a Spectrum Analyzer it is difficult to know EXACTLY what is going on. Obviously the RX can cause no problems but can still be "optimized" by careful tuning.

For the relatively small (compared to the cost of an airplane) cost, it is worth checking to be sure.IMO

Even if you were to fine a problem with your RX, you may not find ALL of them. Let a skilled tech have a look at it and be sure to tell him exactly what happened and what you have observed. Nothing is harder to troubleshoot than: "It just don't work right sometimes".

Good luck.