This is on my '83 300SD with 250k

Have a listen to this:
http://filebox.vt.edu/users/chhill4/engine%20starter%20issue.mp3

The engine turns over once or twice, and I swear it kicks on one or maybe two cylinders, but then it "hops" off the starter, and it spins free (all as you hear in the above mp3. Is this a bad Starter Bendix, or is it normal that the engine will kick once, and pull itself off the starter (leaving the starter to spin free)?

I checked everything involving the glow plugs - all are 0.6-0.8 ohms, and see about 10.35 volts. I had previously found one that was shot (infinite resistance), and I replaced just that one. If all GPs are within spec (ohms and voltage), is there absolutely no need to change them, or might they still not be glowing as hot as a fresh new set would glow?

I am having a lot of trouble starting (read: it won't start) below about 45*F. I went to plug in my block heater, but I measured infinite resistance across all three prongs. Where should I look to find the other end of the three prong plug, and the actual engine block heater?

Thanks in advance for all the help. You guys'/gals' experience comes as pure genius.

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1983 300SD ~250k