I have a 7390 which I foolishly imported from Germany. German 7390s have different firmware and won't let you load the international firmware without a lot of hacking.
Relevant to the OP, I reported a line fault on the voice line and it resulted in a Banded DLM cap. It took 2 months of calls and emails to get an openreach engineer to visit and make the phone call to reset it.
When he visited, I connected the OR modem again and used the 7390 as a router. I switched it back after he left. No comment was made about it.
When he was here, he also replaced the back box of the master socket saying the new OR ones had different capacitors and were better for VDSL. After he replaced it my SNR went from 12dB to 7dB which also affected the speed. He took the old one away - so i cant change it back. Anyone else heard of this?