I know that I have an oil seal leak in the camshaft. I noticed that the oil light stays on for a couple of seconds after the other dash/idiot lights go off. When does the oil light stay on like that, and can I suspect an oil leak under those circumstances?

It's probably a good idea to fix the cam leak if it's at the front. Oil degrades/softens the timing belt causing it to shed teeth and leave you stranded.
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1980 245 Canadian B21A with SU carb and M46 trans

This is normal, more so if you are using a cheap crappy filter like Fram.

The light stays on until the engine builds pressure and fills up the oil filter completely.

With a Mann filter, that light won't stay on for more then half a second.

I would say your leak has little to do with the light staying on.
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If you listen to the radio in Portland, OR, you may know me as "Portland's Favorite Soul Brother!"

I agree 100%. Change to a good oil filter next oil change.
Use MANN or Volvo (made by MANN).
The filters have a check valve in them preventing oil from draining back into the sump. My cars all have oil lights that go out before the engine even fires- almost instantly.
I've noticed the improvement on VOlvo and VW engines- it definitely extends their life by preventing dry running.
No matter how bad the cam leak is, the oil pressure won't be affected by it. You might slow it down however by cleaning/ replacing your flame trap. That reduces internal engine pressure, preventing seals from blowing out.
Good luck.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 230K, 88 744GLE- 220K, 82 245T-181K Also responsible for the care and feeding of: 88 745GLE, 231K, 87 244DL, 239K, 94 855GLT 189K