One of dozens of LP side spin-on fuel filter posts from 6 years ago.

Now Andy's filter is different to mine but the cause + affect is exactly the same. The suction-side diesel fuel filter is always upstream from the tank and the fuel flows by vacuum through the filter as opposed to Andy's where the pump forces fuel under pressure, through the filter, so :

- loss of vacuum caused by air leaks
- air introduced into the fuel system could result in lower fuel delivery
- old + new 0 ring
- dry not lubed 0 ring
- slack [vibration] filter
- slack water drain tap
- dirty filter
- housing itself cracked

Busy garage, trainee does a service, radio on, gets distracted forgets to check 'nip up' tightness on filter can / water trap and all hell breaks loose.

Check the easy / cheap / DIY things 1st - hard expensive engineers later if you need to.