I fly only 72MHz with a 9CAP with no issue using good Rx's so far. The only thing you didn't swap was the TX
If you have a dial a crash like I use recheck the frequ you are set to and try another frequ. The seeker is X'tal-less isn't it, if you are moving x'tal from rx to rx that could be the culprit.
The motor could be the culprit too if it has bearing that are going out metal to metal is the kiss of death to 72Mhz