I'll try the glowing for 30 seconds and see if that helps.
Plugs are only 8 months old.

No WVO in the car in months and both filters changed after this started happening to see if that was the problem. Didn't change it at all.

The hard starts happened suddenly. One night I put her away for the night, the next day she was hard starting.

She's never been picky before but tonight I plugged in the block heater. Wonder what will happe in the AM.

Starter sounds peachy. Turns fast until the battery starts to lost it.

There was a small problem with the ignition for a while. The glow light wouldn't always come on. I'd have to turn the key several times until the light came on to start it. To my knowledge the car never was attempted to start unless the glow light was on. That prblem fixed itself and the light comes on every time.

If the plugs are less than a year old, could it be the relay?

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Ginny in Denver-ish
78 300SD, 265K (mine)