1980 MB 300SD WILL NOT START BELOW 30 deg F.

All New Glow Plugs and Double check GP system, thanks to Diesel Giant. ALL SYSTEMS GO!
Battery checks at 12+ volts not running.
Charge checks at 13+ while running.
Both filters changed.
Fuel vapor exits tail pipe while attempting to start.
Fuel Lines purged using replacement to stock prime pump.
All petro in tank. (no WVO)
Warm Compression Test results - 280, 290, 305, 310, 310.
250K miles
This car starts immeadiately in warmer weather (40 + degrees).
Shows a little hesitation between 30 & 40, but below 30 is a NO GO.
No amount of GP cycles seems to help.

What gives? My starter is new as of 4 months ago, but seems to turn the engine slower in the below 30 degree temps. It is hard to tell seeing how quickly it ussually starts, I never got a good feel as to how fast the engine turns without an immeadiate start.

I wanted to check you all before I go and drop $260 on another starter. Any Ideas? Thanks in advance.

Noel