Some designs you get cross talk. Some did a good job minimizing it. The ones that bleed the tuner across on the tape monitor get in the habit of switching to aux or phono where there is no source coming in. Can get irritating playing a cd or such and in the quiet sections can hear the radio in the background.
Just did some work on a TX-2500 I gifted to a friend a few years ago that was dropping a channel. Spent the last week or so running it to see if it would drop a channel again behaved itself. I don't remember having a problem with FM noticeably bleeding across to the tape monitor on it. Since it has no AUX was feeding my mp3 source through the tape monitor. I had touched up a few questionable solder joints at the function control and gave the pots and switches a good cleaning to hopefully remove the cause of the channel drop. Behaved
I take it by the Mk I you are referring to this one:
View attachment 1766692