ok, i had begun a very useful emil exchange with support about this, but, awaiting for another reply, i actually did a bit more digging and 'solved' the problem.
after the amazing new syphon was released, i followed some links and thought it would be interesting to have "untiy" app on my system. this is ironic because i am on 10.5.8 and syphon requires 10.6 anyway, but i keep meaning to update.
looking in my c74 externals folder, i noticed that all my native max externals had a plain white icon instead of the usual max external icon. getting info on one of these i noticed that the unity utility app "unitron" had taken over all max externals since its install. it had made max externals turn white icon, but not affected the usage of these inside max itself. however it had turned all third party externals into blue mac os folders and prevented them from loading in max. as if it had 'uncompiled' them somehow. weird. i simply reset the 'open with' command, chose 'change all', dealt with a computer crash, restarted, did it again and now EVERYTHING is back to normal. the third party externals, which had become openable folders, are no longer folders but proper externals again.
any further thoughts from anyone would be great. but at least this is maybe interesting in case it happens to any other such tools as me.
sorry for all the noise in general.