Common cause of boost leaks. Only exists on 6 speed cars up until 2001. Tiptronic and cars M box and newer do not have F-hoses.
Part No: 078-133-784AJ
Number 28 here:
ECS tuning carries the Samco F-hose.
Part number 078-133-784BG is listed for the AZB, and is probably not an F-hose.
Note that when replacing the F-hose, the coupler (number 29, part number 078-133-587) is very brittle and might break.
Fortunately, it is NOT a check valve, only a coupler, and can be replaced by random parts and some teflon tape.
Alternately, ECS tuning carries replacement couplers.