RICHARD - You didn't give any specifics but on earlier CC's, until about the mid 1970's the scissor linkage on the mule drive rode on the rockshaft and wore a notch like You described on mowers that had been over COUNTLESS acres of lawn. I've welded up My rockshaft on My 72 twice in the 28 yrs I've had it. The last time I modified the scissor linkage kinda like IH did on the mule drive for the 44A deck I had on My 129. Instead of the edge of the 1/4" thk arm wearing thru the rockshaft I put a piece of 1/4" thk X 1-1/4" wide steel on it to bear on the width of the piece instead of the edge of the piece. The wear has slowed DRASTICLY.
Groove in Your rockshaft may just be normal wear & tear, not the act of a prior owner.
I've been around IH equipment of ALL types, tractors, trucks, combines, corn pickers, plows, discs, ALL kinds of farm equip, construction & indstrial equip. and Yes, They did have some VERY good Engineers, but they were spread VERY thin working on all kinds of projects decades ago as the company was structured. Plus their marketing dept. was relentlessly pushing them into new markets trying to design SPECIAL equipment for special conditions they would only build a few hundred units for over 10 & 20 years. The would design 60 & 80 HP ag tractors using basically a 36 HP tractor drivetrain with legendary POOR results. IH didn't just want to compete in the market place with JD, or CAT, or Massey-Ferguson, or Ford....NO, They wanted to compete and beat THEM ALL, on tractors, trucks, combines, garden tractors, all tillage & harvesting equip. When IH put the resources necessary to a project they had great results. When they didn't or they hurried because Marketing wouldn't let them test long enough for durability they suffered. They were truely a WORLD CLASS manufacturing company, especially from about 1900 till about 1950, even into the 1960's they probably had the Highest percentage of in-house mfg. parts of ANY company in manufacturing. They not only operated MANY foundries to make iron castings they also had their own steel mill and forge shops, and two iron ore ships on the Great Lakes, and their own logging operation to make lumber used in quite a few of their product lines, and they made their own coke to operate the furnaces at their foundries. They made their own carburators & magnetos and distributors. They just tried to make the old FARMALL H & M tractor for too many years into the 1950's and the competition caught up with them. After about 1957 or 1958 IH never had the largest selling ag tractor in the US again. And lots of their other product lines were revolutionary when they first came out with them but they built them without changes and improvements WAY too long.
That all said, about 1968 when IH released the CC 72/104/105/124/125 they set the high water mark for design on garden tractors. The 70 & 100 were great tractors also.