<sigh> Another "240D Won't Start Thread"

[Redpeople]

A bit of background:

I've owned my 240D for a couple of months, and it had started and run beautifully up until a few weeks ago (when it got cold). Over the last few weeks, I've had two instances where it wouldn't start after being left out for the day in 10-15F temperatures. The first time, I was able to start it when it warmed up the next day. Last week, I had the same problem and wasn't able to get it started even after a few days. During that process, the pre-glow eventually quit working (no light and no glow). I had it towed home to my garage.

After some initial misdiagnosis, I determined that the #4 glowplug had burned out, breaking the circuit and preventing any plugs from glowing. I replaced that plug yesterday, and the pre-glow circuit now works (light back on and power at all the plugs).

However, it still won't start. It starts to fire, but won't catch and keep running. The temp in my garage is probably 35F, and it previously had no problem starting at that temp.

I have noticed one thing that is different. Whereas before, the pre-glow light stayed lit and glowed solid until it turned off, it now glows solid for maybe 15 seconds, then starts to flicker a little, then goes mostly completely out with just a little flicker. When I go to crank, the glow light comes back on sometimes and flickers off and on.

In the interest of full disclosure, the replacement glow plug was the universally reviled Autolite brand. I ordered it over the phone from my local NAPA and didn't realize what I was getting until it arrived a few days later. Still, I wouldn't think it would make that big a difference. Maybe I'm wrong.

Where do I go from here?