Having patchy reception from digital radio (mostly D1 band stations) on my Bolero system - for large chunks of my commute the signal goes dead. However, I had an aux-in adaptor in my old Fabia Mk2 (https://www.pure.com/uk/car-audio/products/highway-200) and this worked fine with no signal drop-out on the same routes.

 

Could it be that the aerial on the adpator is better than the one fitted in the car? It was one where a magnet fixes to the roof and then the aerial sticks to the windscreen. If so, can the aerial from the adaptor be used to replace the aerial which is currently plugged into the Bolero? How would I fit this?

I don't really know about the aerial, but just checking nothing else has changed... like a dashcam or other plug in/powered device that could cause noise? If so, could try a ferrite core first https://www.amazon.co.uk/s?k=ferrite+core&ref=nb_sb_noss_2

One quick and cheap way to check if it is the DAB aerial or wiring is to replace that aerial temporarily with one of the ones that Halfords sell, then take it from there, I did that when I replaced a non DAB radio for a DAB radio while waiting for parts to add a new aerial. The DAB aerial should have its own connector on the rear of the radio so swapping over would work, I did not even power up the Halfords aerial preamp and it worked okay in a marginal area for reception.