<VV> Head studs - how bad to need replacement?

[Les]

Hi,

Working on a 140 here. All the upper studs are in place BUT - all the 
upper studs on one side have the threads missing (rusted away) above 
where the nut covered the threads.


Should I replace these studs (that are all solidly attached to the 
block) or just leave them be?

Les
corvair at mts.net
(VV since 1995)