Take it apart and clean it, the first that comes to mind is the ram or linkages are binding. And you will not know until it is taken apart.
I had to take my 1973 RCBS Rockchucker apart and the problem was reloading in the basement and the humidity.
And steel wool and Kroil cleaned up the slight corrosion on the ram and other parts. The other culprit was depriming primer residue inside the ram area and gritty resistance.
Now every year the press gets a Kriol bath to flush and clean the recessed areas. And now I lube it with a mix of synthetic motor oil and transmission fluid etc. This was AR15 bug juice designed to lube the AR15 (running wet) but I didn't like the smell of the hot oil and went back to CLP.
NOTE: The transmission fluid has a lot of anti corrosion ingredients and the main reason I use it to lube the press.
Besides the STP makes my press go faster.
Excellent, Cheap, and Homemade Gun Lube
This is a formula called "Bug Juice" we learned at an NRA Instructor School:
*2-Quarts Synthetic Motor Oil. We used 10-30 but weight ain't really important.
*1-Quart Automatic Transmission Fluid. Brand and spec. don't matter.
*1-Bottle of original STP. The blue bottle.
*1-7 oz. jar of Hoppe's Solvent.
http://forums.officer.com/t135655/