I’m sorry if this has been done, but the roof is not knackered, it needs some TLC on the complicated joints.
When the roof was done it was designed so that the plastic man proof sheets hugged up to the metal frames that are the roof support. These would be sealed with a system called Kemperol. This a good system if done correctl. Unfortunately it wasn’t.
it’s a system of liquid added to a primer and put of a bandage system that sticks and seals for about 25 years. Google it if you are bored.
I spent 3 months on the roof fixing what a few useless lads had laid. That was 21+ years ago and some of the suspect joints have now weathered and gone past their sell by date.
The sheets are fine, it just needs someone to come in and fix the leaking joints. There is no point for disturbance on the joints that are ok. But you only find the leaky joints when it’s raining.
I no longer roof for a living, so Sorry to have bored the crap out of you.