Swear Meter Rating of 4: Removing too many things to get somewhere sucks.
Two things that made me sweat as a new DeLorean owner more than anything were the rumors of how hard it was to do two things: 1. replacing the dash speakers, and 2. replacing the mode switch seal. Far from true, this was kind of a piece of cake if you take it in stride and know what you're up against.
If your mode switch (the one that says where the airflow is going to go to your vents) hisses like mad all the time and takes adjusting to get it to stop, you may need a new one. The seal itself is about 1.5" in diameter and takes about 5 minutes to replace once you get it out of the car. But there's the trick.
The switch of course lies in the very center of the center console. It's buried under 35,000 wires behind the radio bracket. Unless you've got TINY hands I recommend you partially remove the center console piece. Doing this of course requires removing a bunch of screws and bolts, most of which have their very own washer! What else is new.
For reasons I now don't quite understand I first removed the vents. Maybe I was curious.. I don't remember at this point but just don't bother with it. They were a PAIN to get back in. It involved a long flathead screwdriver and a lot of sweat and zen-like patience. I don't count it towards the swear meter because it was a totally unnecessary thing to do. Anyhoo...
First remove the a/c panel plate. To do this you need to remove all the knobs from the switches. Try to remember where they were pointing :) The center knob (mode switch) reveals a single screw holding the plate on. Remove and set it aside carefully. Now would be a great time to replace a dead light bulb if you've got any.
There's two screws holding down the shifter plate near the switches, then two bolts holding the console set to the underbody near the front, some right at the corner of where the shifter plate goes, and then if you remove the little tray near the back there's yet two more screws holding it together. I forget the size of the bolts, a metric 10 I think, but you'll figure it out. A ratchet with an extension is priceless for this work, and the little tray, once removed, is great for holding the bolts/washers. The center console is also affixed to the dash pads on both sides with some black phillips head screws - remove them as well.
Gently lift the center console upwards and backwards. Be careful of the electric lines and pressure lines underneath it. It only needs to go up and back enough for you to get your adult-sized arm up behind the radio bracket.
As a matter of precaution I removed my hazard light switch from its socket so it's out of the way. The second screw holding the mode switch to the bracket can be removed from the front. The switch itself isn't held on by much so it will almost fall back inside there. A rubber hose bundle attaches to the back. It only goes on there one way so you can't screw up putting it back on. It's also attached with 3 spring clip wires. Take note of how they went, I'm pretty sure it's important. It's why I took that picture. Hurrah! The switch is free!
I'd recommend replacing the seal someplace cleaner than around your car, but that's just me. Anyway the switch itself is fairly simple. The seal directs pressurized air to where it needs to go. If it gets dried out it no longer seals, hence the hissing.
First remove the two philips head screws holding the top part to the bottom part. The little plug in the middle is what holds this whole thing together. With the greatest of your skills, get a pair of needle-nose pliars and gently work that plug out of its place so the seal will be released. Along with the plug there is a large soft spring that will come off. Once apart, the seal is simply attached by its setting in the little plastic plate. Pop it off and put in the new one. Lubrication is a topic of debate, I put a little sliver of vaseline along the ridges of mine, not sure what the verdict on that is to be honest. Go look it up elsewhere :)
Reassemble with the spring and clip and put it back where it went in the car, making sure to reconnect those wires the right way. Be careful when putting the console back down, as there are lots of things to get in the way of a proper seating. The switch should "click" if it's all back together right. Mine didn't click before I replaced the seal, it just hissed a lot.
There are several DMC vendors that have this switch seal available. The price plans vary greatly, and it depends on what other things come with it. DMC in Texas offers a new copy of the plug. If your tabs are broken (or if you broke them, dummy) the part comes with the replacement seal. PJ Grady includes the seal, pre-lubricated, and also has a longer screw for mounting the mode seal switch. SpecialTAuto.com offers the seal at an excellent price with no accessories. Some vendors may replace the seal for a core swap as well.