If the fuel pressure is okay (checked in the manner previously described), then the return line is fine. If the pressure is too high with the new FPR, then the line is likely at least partially obstructed. (Obviously, if air passed through the line to the tank, it couldn't be completely blocked.) Physical inspection might reveal damage.
[...]I’ll also look at rechecking the “fuel pressure” with the new FPR as well as the vacuum. Is there any other way of checking the return line other than what I did (blowing air at the FPR and listening at the fill pipe for the gas tank)?[...]
Unfortunately, it's probably not something you'd be inclined to do yourself. To see what's involved, look at the FSM section "Engine", file "valve clearance.pdf". Before the 2003 models, Subaru specified a 105,000 mile interval for checking/adjusting the valves on engines with mechanical lifters (hydraulic lash adjusters, or HLAs, don't require adjustment).
Another thing mentioned in Post # 198 was “valve adjustments”, I’m not aware that the car has had any and like I mentioned in the beginning is that we bought this car brand new in 2000. I have to admit I’m not familiar with this and do not know what is involved with valve adjustments.
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