Thanks, that is kinda what I thought. Just aging.
On the crack repair, I have done a few standard '68 wheels. On the repair, here's my take (which may or may not apply to your fixes).
Most of the write-ups I see show cutting the old crack at 90 degrees to the wheel. This leaves the bonding face right along the same area that originally cracked, high stress, and the area is as small as possible as a "donut" around the steel core.
I cut back the crack at a wide "V", say the crack is 1/4", I'll go 1 1/2" -2" wide at the top making a wide "V" (yes, a lot of removal, freaked me out the first time I did it, but the results are good).
Use a high quality body filler. Fill the gap, sand to recover the shape. The finger grooves are tricky, but not too hard.
Sand, prime and paint. I have done 2 I still have, one 8 years old, and gone thru serious heat here in Brisbane, but not freezing cold. Perfect. Same for a 5-6 year old one I did.
The big groove puts the strain on the patch over a far larger surface area. And puts the forces in some shear across the bonding surface, not direct strain. Which makes it less likely to recrack. And the high quality body filler has some "give" to it, so not a 100% rigid item as with some other fillers, more likely to crack the less give they have...
Small areas on the backside are harder, but again I grind out a fair bit of material to get as good a surface area as possible...
HTH