Just bought a 01 1150 that has been off the road for a while I now have the tank off to do the fuel filter question should I be doing anything else whilst I’m in there??
At that age unless its been done previously the little 'U' shaped rubber pipe inside the tank that goes between the filter and the pump if memory serves me right. Part no. 16142325808. They can look okay externally but can fail inside and split but as the pipe is submerged in the tank there's no external sign of leakage. It is special rubber as it has to be submerged in the petrol and looks expensive but well worth doing if you're in there anyway. Don't be tempted to overtighten the tank hatch nuts when reassembling, even if one of the studs snaps off.
If they look like the originals replace the fuel pipes. From experience there's nothing more scary than when a perished line bursts and pumps neat fuel all over a hot engine. And worth installing quick release connectors on the new pipes too as you're bound to be removing the tank again at some point in the future...