C4

I have a huge C4 tranny leak. It leaked before "rebuild" and still does. I think its the converter ... but ... I can't find any that will fit. Oh, its a 66, 200 CID. I see they sell repair sleeves but can't imagine that big a leak (a pint in a week or two) could be the sealing surface... but I don't know. Any suggestions / help?
Thanks,
Clint

Thanks HS,
Should the fluid in the converter runs back into the case while parked? I would think that the fluid in the converter should stay there, but I am probably wrong. I know the thing has to come back out and I'm not wanting to do it. I will try to do it without pulling the engine. Ugh!
Clint