I just got the Supertool 300 from Leatherman. They said they no longer have Replacement parts for the OST. The ST 300 tools are definitely more robust and I like the unlocking feature. However it is a lot more bulky. That's my only real complaint. Also it seems to be VERY stiff to open and close. Very tight tolerances. My OST I could swing open like a balisong in an instant. I'm sure the ST 300 will be that way after 15 years of use too though.
As to the weight of the Surge, I've considered that and actually I don't think t would other me. I'm still considering trading my ST300 for the Surge just to try something new. I just cant decide.