I've just completed a complete teardown of my 87 coupe's engine. I had just gotten it running after the previous owner confused the plug wires and tore the flywheel apart. It had a coolant leak somewhere, but I drove it about 5 miles after I noticed it (trying to get home). I'm an idiot. I muffed up in a bad way. Long story short it was pumping a steady stream of water out of the exhaust; wouldn't idle but would start and run at high RPMs (Yeah, I should NOT have done that either). So I let it sit 3 months before I tore into it. Did I mention I'm an idiot?

TL;DR: I'm pretty sure it was a blown coolant seal, now there's a little rust on the internals. My questions are:
1. How do I locate the leak? I've roughly inspected the seals and noticed a couple of spots with wear/tear
2. How should I go about getting the rust off? I've seen suggestions like kerosene, a parts cleaner, and emery pads. Are all of those viable suggestions? Would it get the rust out safely?

I have several pictures of the internals. What's the best way to get them up if you guys wanna see?

 

I'd bow to one of the builders that come on here occasionally. But housings, if chrome isn't flaking or worn beyond spec, shouldn't be terribly affected by the water. Clean them up, maybe a little soak in white vinegar.
As for the irons and rotors, I might try the vinegar on the irons, then rinse in water then hose down with WD-40. Repeat as necessary. Carbon deposits won't come off with vinegar but it should remove any superficial corrosion. For carbon on the rotors I'd glove up with eye protection and used EASYOFF oven cleaner with a nylon scrub pad. Remove the old side and apex seals and use them to scrap the seal grooves clean of carbon. Rinse in water repeat as necessary. Then thoroughly hose down with WD-40. If your irons are pitted they're junk and you'll just have to source new ones.

 

The plates looked good from what I could discern. Some spots on my rotors I thought looked the worst. I'll be getting some vinegar and oven cleaner tomorrow. Thank you!

 

Be careful with the irons they can look good but be very rotten. Be suspicious of any discolouration

 

Thanks for the heads up. If I notice anything suspicious and search didn't help, I'll be back.

 

Search?
All spec's are in the Factory Service Manual.

 

a brass brush and your arms.

getting the side seals out will be the difficult part, there is some procedures for doing that on here if you use the search.

 

Naval jelly to dissolve the rust. But only if it is surface rust. If you are seeing pitting in any of the seal grooves then the rotor is unusable.

Same with the iron. A light surface rust is fine. Pitting, depending on where it is, may make the iron unusable. Housings get severely worn when pumping water as well. If there is any chrome flaking then water gets in there and starts rusting.

As for finding the leak, check the housings and irons for flatness.

On the S4 there is a weak casting on the front and rear iron at about the 5 o'clock position. Check for cracks in that area and examine the entire seal groove for cracks/deep pitting.