Darren,
Usually the topslide and crosslide use left hand threads, so you would need to take them out to check. Also you would need to find the pitch, otherwise your handle scales wouldn't tally to the movement obtained.
You can usually get away with just replacing the nuts.
The nuts are usually made of bronze, to take the continual stresses and wear. I have made these myself for my old Atlas lathe, but usually I make a slight modification to adjust out the wear, and it doubles the life of the leadscrew nut, but it depends if you have a little room spare around it. If there is enough meat on the old ones, you might be able to do the dead easy mod, and it would keep you going for a couple of years. I have a couple of acme taps, you would need to find out the correct size.
With regards to coolant, I used these on my old lathe and mill, and are about the cheapest you will find anywhere.
http://www.axminster.co.uk/sessionID/QOL/recno/1/product-Axminster-Coolant-System-21084.htmThey do extend tool life considerably, plus also the workpiece doesn't heat up as much and change properties half way thru machining. But goggles and apron are a neccessity, otherwise you will get rather wet, unless you fit splash guards. It is a basic system, but works well.
BTW, the mill drill that you have is what I had been using for the last ever so many years until I just upgraded. I managed to make a few nice pieces on mine, and never gave any trouble at all. It coped with everything, including this chopper frame in for modification.

Problems are usually in the mind, not with the machine.
John