I too have an old D-2V - man, what a "classic" - and can't think of any reason not to clean the condensers. If you use a window cleaner, just make sure it does not contain ammonia. Explanation "why" is too long - just take my word for it.

I used to make my own cleaner for my telescope as follows, and it is probably the most benign cleaner you can use.

2/3: distilled water

1/3: 90% isopropol alchohol (rubbing alchohol - but not the stuff with a lubricant - that's mineral oil)

2-3 drops Photo Flo.

Add the ingredients in the order listed. Agitate gently (so as not to foam the Photo Flo) and you've got a great cleaner that won't hurt optics.