Is my regulator faulty?

I have been battling inconsistent carbonation for a while now. I have checked for leaks in the system and everything seems fine. On some occasions I go out pour a perfectly carbonated beer with excellent head, the next time I try some it's flat. Sometimes it seems that the first pour of the day is perfect, and the following pours are flat.

On my current beer I naturally carbonated for a few weeks at room temp and then put the keg in the fridge. Fridge temp is 38 degrees, 9' of beer line @ 15psi. I let the beer chill for a day and came back and had a few perfect beers. A few days later some friends were over wanting to try the brew, and it was flat with very little head. The regulator still reads 15psi and had not been touched since the keg was installed.

Does it sound like my regulator might be to blame? It's pretty ancient so I am not opposed to replacing, but don't want to buy one if its likely not the cause.

or maybe I am faulty?

Try turning down to 10 or 11 PSI. I was carbonating and dispensing at 15 PSI and 10 feet of beer line and my pours were inconsistent. I think the fast pour was causing the CO2 to come out of solution leaving me with a ton of head and not much left in the beer.

Will give that a shot, but would that also cause no head / flat beer? I'm not really having foam issues (anymore thankfully).

Thank you for your response.

I'm not sure, but the only other thing I can think of is some sort of leak. Have you tried spraying down the fittings/gaskets/posts with soapy water yet?

Yep, I've tried a few times with no sign of leakage. I am thinking that since I naturally carbonate and keg condition, the first few good pours may be a result of the natural carbonation process. As I dispense the beer, the regulator does not accurately control co2 levels in the tank and eventually the beer falls flat. Does this sound reasonable? It is a really ancient regulator that came with a box of stuff from craigslist, so I am not sure how accurate the gauges are.