mercedes c250d 1993 drawing air?

[rustybucket]

hi,i have recently purcased a late 1993 c250 diesel.it was running fine untill it just cut out.when turning the key air bubbles can be seen in the clear pipes at the filter.i had it running by pouring fuel into the filter from a bottle but as soon as i connect the fuel line again it starts to draw air.where should i look first?,is there a common fault?please advise.
thanks

 

[Bumper]

There seems ro be problems with the 'O' rings.

have a look at this link it may help

http://forums.mercedesclub.org.uk/showthread.php?t=13271&highlight=diesel+leak