Anyone know much about this part?
 

I was looking through QuickServe for some fuel parts and came across a listing for a "check valve" banjo bolt that appears to screw in on top of the fuel filter mount and holds down the return line from the injectors. Has anyone messed with this or had to replace it? For all the problems the overflow valve has I'd imagine this has had to contribute to some degree. It appears to be a very similar part.

Got that pic or page number off quick serve?