It sounds strange with a pristine bore but fouled chambers (pitting from storing loaded for years?).
From the serial number it is probably 1978, maybe 1979.
Mine was s/n N237801, and per factory Letter it shipped October 13, 1975 to Maryland Police Supply Co. in Baltimore, MD.
I sold mine a few years ago to another Forum Member for $750 shipped so Your LGS asking price is not to bad for these days IF the chambers check out equal to the bore. If not there maybe other problems internal (rust, bad timing or carry-up). These were basically cop guns so should have a fairly significant trigger pull weight in both SA and DA. Look for case head impact on recoil shield also if a lot of Magnum rounds went through it.
Also...if barrel condition with pristine bore, no muzzle wear, excellent looking forcing cone doesn't match cylinder condition with normal high spot wear, then look for any "bubba" marks at the pin attaching bbl to frame. If signs of trying to remove and replace, finish upset, not proud, etc. ) then maybe barrel is a replacement for one heavily worn.
Good luck and let us know if you get it (with pics).

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I've owned 28's & 27's for over 40 years........Never, ever have I felt/saw/handled or heard of these guns being cop's gun with heavier SA/DA trigger pulls...........Taint so.