Greetings board!

I have a wonderful '81 240 DL that has one glaring flaw:

It runs like a champ for about 2 weeks at a time, and then
just won't start. There is no warning. The starter motor whirrs
but the engine won't catch. Every time it happens,
I get it towed this place or that, and when it has reached where it
is going.... it starts. It has been like this since I bought it
(1.5 months ago) and no mechanic can pinpoint the problem.
It's like clockwork, every 2 weeks or so. The last time it happened,
it did it's no start thing when it was still warm (every time
it did this it was a warm start except for this last time)
and I let it sit for 3 weeks. The battery was dead when I got back
in. I got it towed, garage charged the battery, and it started
right up. It is leaking oil, and the alternator is covered with it,
but it still won't start even with a jump.

Any help is fantastic!

Regards,

Pete