Sliding barn door is really tough to open

Hi everyone.
I've got an amateur problem.  I have a pretty big (approx. 15' X 15') and really heavy sliding door on my barn.  The darn thing is just so stiff on its rollers and I'm killing myself opening it.
I had to have the track repaired a few years back and the guys who came out lubed it up so I could open it with one hand again.  But since then it's just gotten more and more stiff.  I'm afraid something will jam up and break.
But I can't for the life of me figure out how to get lube up onto the axles of the rollers.  A can of spray lube and nozzle from the outside doesn't seem to want to reach the right spot.  And I've tried to slide a can into the track  from the end and aim the straw from the nozzle at them but it keeps popping out of the nozzle.
I anyone has any tricks or knows what kind of special equipment I need to get at them, please let me know.
Thanks

I'm posting a couple of stock photos of the stuff I'm working with.