I really don't think heat or lubrication is much of a factor... They are supposed to be a press fit, and not move at all. I think because of the spiral wound design, with very thin material, they are flexing and getting work hardened under heavy use.
The repair I proposed above is very effective... I don't remember what brand or model trans I saw it done from the factory on, but it certainly made an impression when I attempted to disassemble it...
I grabbed an old 5 speed fork today and took some pics for a demonstration of what I'm talking about.
First the factory spiral wound pin. You'll want to drive it out:
http://i90.photobucket.com/albums/k2...ps5e184239.jpg
Then enlarge the hole to 1/4":
http://i90.photobucket.com/albums/k2...ps5105901b.jpg
Then install the 1/4" single wrap spring steel roll pin:
http://i90.photobucket.com/albums/k2...psd32832ff.jpg
Then install a 5/32" pin inside that one:
http://i90.photobucket.com/albums/k2...ps1d39edd0.jpg
You'll notice how the 5/32" pin is mushroomed after install.... That's because I had to beat the crap out of it to get it in. Obviously a press would be a better install tool, but I was simply trying to perform a demonstration.
This thing is not going anywhere... Ever... Just for giggles, I tried to take it back out. I broke my punch...