It's electronics. Values of electronics can change for several reasons..
Mostly due to heat.
But, it hard to say. I have never heard of other users having this same issue with the spectra.
I have had my Spectra module for over 4 years with no issues....
I have been running the Xxtra rx's since they came out also...
However, I do like the DCX & HIS-03MK Rx's better.