Ariens S-16H lift problem

[Natureboy]

I just bought an S-16H Model#931018 and am having a problem with the lift system. Front lift for snowblower works most of the time, rear 3 point lift works all the time, but center rock shaft will only come down a little than snap back up. Tractor runs good, takes hills with no problem, but I cant mow without the center rock shaft. I checked the Ariens repair manual online, but it doesn't address this problem. Anyone know what I am overlooking? Thanks in advance.

 

[Natureboy]

Found the problem after cleaning away the grime. The slotted hole in the shaft is so worn that it only goes so far than snaps back.