If your core support is rusted thru, it really should be replaced.
If it is minor surface rust, then it can be cleaned and painted with POR or a similar rust preventative.
The core support
helps hold the front bodywork in alignment, so it needs to be fairly solid. A lot of supports do rust on the bottoms, because they tend to collect water down there.
______________
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"