"worth" strikes me as an adjective after a linking verb:
        The treasure is worth 2 million.
 
        Consider: a) The treasure, worth 2 million, was never found.
                  b) The treasure, having a value of 2 million,...
 
        It is hard to see worth as a verb in a) above; instead it
seems to function adjectivally, like "having a value." Of course it
can also function as a noun: His worth declined...
        How would you conjugate a verb "worth"?
 
        I worth
        you worth
        he worths
 
        Perhaps the grammar sheet writers confused 'worth" with
"value":
        c) The treasure is valued at 2 million.
 
"Value" is a passive voice verb in c). "Value" can be conjugated:
 
        I value
        you value
        he values
                                       --Bill Murdick