I use lapping compound on the input shaft and clutch splines… sliding them back and forth until they move freely with no hangups or tight areas.
I looked at an image of my input shaft, (image below) 300M material, and while the image isn’t as up close as the OP’s, I don’t see the chatter marks, which could only come from the spline machining (cutting/rolling) process, or from clutch binding. If it were clutch binding, it wouldn’t be in the bottom of the valley as much as the walls of the valleys… I don’t think a cutter wheel would leave chatter marks like that, but I’m no expert… I’ll believe however, that for the clutch to bind enough to create chatter marks on the input shaft, regardless of material, the car would be basically un-driveable…
I also put a very thin film of lubricant on the input shaft splines… Thin enough such that the uninformed wouldn’t feel it…
And yes, I realize the shaft below is twisted… Builder of the trans said it could not be done, not with 300M material… I proved that hypothesis incorrect… We also as it turned out had twisted the internal shafts, the main shaft so badly they couldn’t remove some of the gears, so they chucked the whole shebang and started over…
Dead hook at 6500 rpm, Lucas Oil Raceway, the week after the US nationals… Track was sticky… my fault entirely…
Twisted shaft, 300M material, shaft is also significantly bigger than stock.
Input shaft, quad disc clutch hub and lapping compound as I start the process.
Repeatedly sliding the hub, feeling for any imperfections or hangups, as per the manufacturer.
Lapping completed, doing final cleanup and stack up, preparing to install…
I apologize for drifting off topic…