Mk3/4 Radio Power Cycles

Just to note, I don't know much about cars!

Have a Mondeo Mk3/4. It's a Mk.3 but has Mk.4 parts, so post-facelift? It has a Sony oval Mk.4 radio, identical to this and it constantly power-cycles. It starts up, stays up for a few seconds, then cuts out and starts up again.

What I've done:

My first thought was either a bad cap or a short somewhere. The aerial stalk was pretty old and weathered, so I replaced the aerial base and seal with new ones, taking apart the overhead console to do so. It was a bit rusty in there around the bolt holding on the aerial base, but nothing unexpected in a car of this age and no evidence of real water ingress. Didn't seem to help.

I pulled the fuse from the radio for 10mins+ to make sure everything was drained. Putting it back in and starting the car, same deal. I did end up pulling the fuse and leaving it out for a few weeks as it was annoying, starting up, getting a few secs of untuned FM radio, then dying again. Eventually I put it back in to test and all was fine for a few months. At this point, the roof aerial was not attached.

Here's the real odd one; through experimenting with taking the aerial off, and when driving around, the reboots only happen when the radio gets DAB reception. If I leave the aerial off so DAB reception is very bad, or when driving through a tunnel, it's fine. Stays on.

I'm happy to pull the unit and see if I can find any bad caps or hunt for shorts, but does anyone have any ideas of what it could be so I'm not going in blind?

Also, I'm fine with replacing the unit myself (watched a handful of videos so now I'm an expert), but anyone know if I'd have to replace like-for-like, or if getting one of the fancier Mk.4 radios like this one would work? I'm not particularly interested in Android Auto or Apple Car or anything.