diff lock

Hi All - I have a 2005 Massey 1528 with the HST and a 1520 FEL. I recently purchased the tractor and have been combing through the unit, everything is seemingly good but when I tried to engage the DIFF I could not tell if it was working... the lever (right above the reverse pedal) seemed to be...

I have a 2021 CK3510SE HST. The darn diff lock lever below the left side of my seat feels stuck. It's been that way in the three months that I've owned the tractor. I've stepped on it, pushed on it by hand, tried it in gear, tried it in neutral and tried it after rocking back and forth a bit...