Exhaust Leaks.... 65 CDV

[Johnt_501]

#1 I’m a new member and I thank all of you for letting me in and for all the future help that I’m sure I will need.
Now to the issue at hand.
I have had several exhaust leaks from my 65 429 CDV. I replaced the gaskets a couple times until I found a small crack at a bolt hole. Then I bought and installed a set of Sanderson headers. All was well for about a year and now I have a leak at the passenger rear side.
The header instructions said to NOT use gaskets, to use high temp (black) silicon.
I know there had been 2 spots on the drivers side that had previously had bolts broke off and drilled out. It appears that the new bold holes were a bit off and the header had to have a bit of material removed at the bolt hole to line the holes up.
The bolts are very difficult to get at with stock manifolds and even worse with the headers.
The only thing I can think of to do next it remove the heads and install the headers while they are off to get the best installation that is possible. And if the heads are off might as well rebuild them but that will not fix the off set bolt hole. * Note: that this exhaust port it not leaking at this time but had been a location of a leak with stock manifolds.*
Or, possibly buying a set of already rebuilt heads just to get original bolt holes and straight surfaces.
Do these motors have a history of leaks? Do previous leaks damage the surface to cause more leaks ?
Any other comments?
Questions?
Suggestions ?
And thank you again.
1965 CDV. 100,000 miles, otherwise runs great. 

["Cadillac Kid" Greg Surfas 15364]

I have ALWAYS used a gasket with headers regardless of what the Mfg suggests.  I would suggest you pull the header, thoroughly clean the head and header mounting surfaces, install a gasket then the headers using locking header bolts to prevent them backing out, the most common cause of leaking.
Greg Surfas

[Cadman-iac]

I also use a gasket with headers, but not those hard paper/cardboard types that are supposed to be for headers. I've had those burn out too easily if there's not enough gasket material under the header flange.
What I use is a stock exhaust gasket, and have never had a problem with these. The only time I had a leak was when a bolt backed off, but any gasket will leak if a bolt is loose.

Rick