RE: Ugly Stck goes in and don't know why??
This might be one of those tough ones to nail down. FM normally goes wild with a contending signal which leaves the thinking that signal was lost for an unknown cause. The cause could be a lot of things such a range problem or receiver or transmitter failure. An antenna not extended, low transmitter battery, loose antenna, receive crystal failure, cold solder joint in receiver, broken receive antenna, receive antenna degraded by close proximity to metal control cable or even a bad switch harness.
The position of the antenna relative to the plane plays a part when range is degraded.
Unless I found the cause, I'd not put the receiver in a valued airplane. It could be crystal, or a cold solder joint and if so, it might cost another airplane.
Not long ago, a guy at the field was losing an occasional plane. Turned out to be a sometimes range problem and transmitter issue. He sent the transmitter in for repair but the problem persisted with another crash so he decommissioned the transmitter.