I noticed this as well. I reached out to Ed Byrnes about it, who believes the elevation cap is original to the rifle. He mentioned he’s seen grooved caps in this range. The cap has also noticeable speckled wear that is uniform with all the steel parts of rest of the rifle. It seems like an arbitrary piece to leave uncorrected.
Regardless, it’s not something I would change on the rifle. The gentleman I spoke to said his father returned home with it wrapped in a wool green army blanket. I know the case of the “buy the rifle, not the story” but he was sincere enough in the sense that he had very little understanding of M1 rifles. I took a chance buying the rifle because his lack of knowledge prevented me from seeing many parts in photographs. He didn’t want to take the rifle apart so I took a chance with the internals and the lower band pin.
I would not change the elevation knob either, but I must point out the reason for my post, is that all the data from Duff's WW2 book and my own data from
Lend Lease rifles show a checkered elevation cap.
Duff's book, sn 421106 and sn 469909 both with checkered cap
Lend lease rifles 380931 and 471665 both with checkered cap
In my old research I found that SA seemed to use up old parts on the LL rifles they sent to England. The few original non-LL examples found in the serial range often have the new version sooner. The rear sight flush nut is a good example, LL guns have them long after the lock bar was introduced.
A little late to the party here but DO NOT USE steel wool, it will ruin the finish. Yoy need bronze wool with some gun grease and a true vintage copper penny, it will knock off the rust spots and not mar the finish. Use these two items all the time to cleam up my M1's and k98's