So the EGR valve and AC have been replaced/recharged. Before I went on vacation, the muffler had come loose somehow so I also had the shop take a look at that.
The shop told me issue with the muffler was that the weld right at the back of the muffler, where the pipe goes into it, is cracked. They said they couldn't really fix it because the pipe and muffler are a welded assembly. It's not going to fall off, it's just rattling around where the weld rusted away.
Upon further inspection I've found the following:
The muffler on my Prelude is
not the welded assembly that the shop thought it was. It is, in fact, a separate muffler and pipe. Probably because of the 4WS gearbox in the rear, that's my guess anyway. See below; a diagram of the exhaust system and a photo of mine. Notice how the diagram says "Optional" parts to the right, which also shows the difference in exhaust tips between the two models (the ones on mine are straight whereas the other has flared ones)... AA and AZ do not have this muffler in stock at the store so I will most likely be ordering from RockAuto. $40 vs $151 for a new muffler, plus less headache installing sounds good to me. Hopefully I can get that clamp off and hopefully the rest will just slide off. That's gonna be the only troublesome part.
I also called the shop and gave them the part number to see if they could possibly get it in before the weekend. Because if I order it online it will not arrive until Monday.
Just a note, the part numbers for this muffler and pipe are WALKER 18262 (muffler) and WALKER 43449 (pipe) with a 1 3/4" clamp to hold them together.