plumbers ptfe tape or bodging tape?
O ring gone? (example on my mates LR200tdi, diesel fuel filter banjo)
Copper washer lost?
I always carry ptfe tape in the toolbox., the plumbers thin white joint sealing tape.
use a foot length,and twist it to form a thin string. Wrap this precisely around the groove where the o-ring should go, to approximately the size of the o-ring. sorted.
Or for example you can wrap it just under the head of the bolt where the copper washer was, or by wrapping it around a suitable former (biro etc),a rudimentary o-ring can be made.
The most effective way of turning petrol into noise without the side-effect of horsepower