javeo, the filter is uber easy to change with the pan off, 2 or 3 bolts and it's off. For a gasket, in the absence of any real gasket RTV would be a good choice. Just makes separating the pan a bit more challenging without a gasket, but it shouldn't leak if done right. Personally if I need to chase threads or repair a stripped hole, best to pull the pan off and do it on the bench if you can, to save getting metal bits in the trans. Much easier as well.