I'm looking at an early 60's D6 for sale. Other than the rust, the tracks are like new(no wear on grousers and bushings) which may have led to it's problem: it won't move, possibly from sitting too long. I've talked to several knowledgeable folks who've suggested using a penetrant to loosen the pins/links to just salvaging the shoes/pads and getting replacement chains. I don't know if a press is required to split the track on tractor of this size. If I pass, the tractor will probably just sit and rust away. 

You say early '60s, that was when there was two D6 tractors available the D6B and D6C. There are several methods to loosen the tracks that will work on both machines. Please provide the serial number and if possible pictures of the tractor.
Craig

It's a "B". With both steering clutch levers pulled back, one track moved when the flywheel clutch (aka: main) lever was eased back. I have pictures on my IPhone but I don't know how to post them on this site.

just use water to loosen the rust.

yes just park it in a wet area with the bottom of the tracks in water and let it set a while

Rickoshay wrote:

It's a "B". With both steering clutch levers pulled back, one track moved when the flywheel clutch (aka: main) lever was eased back. I have pictures on my IPhone but I don't know how to post them on this site.
 

Are you getting any movement of the sprocket on the side that won't move? If there is no movement of the sprocket then the problem might be deeper.
If the sprocket is moving slightly inside the chain you might be able to get the chain to free up by going back and forth repeatedly. Maybe throw some old diesel or penetrating oil (or water) on the links.

There's not a hint of movement in one track, just the straining of the engine as the main clutch lever is slightly eased back. As you mentioned, perhaps the problem is deeper than just the tracks.

I have an old Caterpillar D6B "Operation and Maintenance Instructions" booklet coming in from Ebay that might tell me something about the brake system. This tractor also has hydraulic steering boosters: I checked the reservoir under the seat and I didn't see any fluid.

You did well ordering the O.A.M.I. book it details how to adjust the brakes. Look and see if the right brake pedal is lower than the left brake pedal. If the right petal is lower the parking brake is engaged, to release it press the right brake petal and release the brake locking lever. The locking lever is on the right and back from the brake petal.
You should be able to post pics soon.
I have a spare Service Manual for the D6B that I will sell reasonable.
Craig