2001 Jeep Cherokee Head Gasket leak

Got a call today from the mechanic that my head gasket is leaking and my rear main seal also. I do not appear to have any cooling issues. The guage stays at the half way point and might kick a notch above but the the fan will come on and the temp will drop down just a notch below the half way mark. Oil pressure seems fine as well. I am pretty confident that I can change the gasket my self seeing that it is only an inline 6. I do have a small leak on the ground that only amounts to about a couple drops a day and very little oil loss. Do you have to drop the trans. On the cherokee to replace the rear main seal? If I replace the gasket what kind of issues should I expect afterwards, such as increase in oil pressure and such that could damage weaker parts?