Sorry about the leaks . Most of us have done this more than once, even me. And not all can just pick up a center section and put it in. The guide studs are a good idea, holds the gasket in place to avoid damage which now you have. You can use more than 2 guide studs , 4 would be better. 2 on top 2 on the bottom. AS for trying to do a fix without removing the pig, Screw in 3-4 longer bolts to slide it out on, then dry the gasket and metal seal area off, you then should be able to see where the gasket is damaged, if reparable , then coat that spot with some gasket maker. Reassemble again using a chris cross pattern for tightening . Good luck