[captonzap]

It sure sounds like a coil going bad.
Since you said you had an ohm meter, measure the ohms in the primary, (low voltage) and secondary windings when the coil is cold, and making a spark.
Then run it for40 minutes, or whenever it starts acting strange, and measure the two coils again. If they are different by more than 10%, that may be a clue. This is not a definitive check, because the current is not flowing in the coils, and there could be a break in the internal wire insulation that allows a short circuit when the heat and voltage gets up.
The only way the condenser could be at fault is if it were shorted. You can disconnect the wire and run without it for a while, just to see if that is the problem. It will start to pit the points, so just run it long enough to get home, if that cures the problem.

If there is anybody near you that plays with OLD VW's, the early ones used 6 volt coils, and they might have a spare that you could try. The polarity is marked on Bosch coils.

CZ