Replacing 308 Distributor Seals - What's The Worse That Could Happen?

Wow, that's a lot of steps.
Some of those steps are unneeded, but shouldn't hurt. Using a paint mark to maintain the distributor rotation isn't precise as the plate you'd be marking position relative to can rotate a little on the studs. Probably only a fraction of a degree, though. When you say check the timing, I hope you mean with a timing light. They're cheap as dirt used on ebay. Taping the distributor down, when you're starting from TDC (just note if the rotor is pointing at #1 or #4) is a little much; it can only go in a discreet number of splines in the cam.
There are other threads out there on this, look for 308 distributor seal on the new and old boards. All the directions you could need.
For your questions on steps 4 & 5, when you unbolt the distributor and remove it, the backing plate can be pulled off by hand. It's sandwiched between the distributor and valve cover. You'll need to press the old seal out and the new one in, using proper sized sockets or seal installer. Do that search to find out tricks about using deep sockets the same size as or slightly larger than the camshaft to ensure you don't lose the spring from the seal while installing.
If you put blue goop on that gasket, I'm sure it won't leak, but it's really not needed. Some people like to put Hylomar Form-a-gasket on there (a different more expensive product available at auto parts stores, I think around $10 for a tube), I've just coated the paper gasket with oil.
As for those cork gaskets, I don't know what they're about. I didn't have any and my car didn't leak. I only see one in the parts book.
Be sure to use plenty of oil on all these parts you're installing and it's easy!

 

Don H. -- Here's a cross-section and the TSB for "plugging" the cams (you should check to see if the TSB is done to your car or not). Nothing wrong with making notes and adding extra marks to keep things straight -- as don_xvi said, just make a small mark on the rim of the distributor housing to show the direction the rotor is pointing at disassembly (and don't move the crankshaft) -- there will be only 1 spline alignment for each distributor that repeats the rotor positions -- at PM1-4 the 1-4 distributor rotor will be pointing at either the #1 or #4 internal contact, but the 5-8 rotor will be in-between contacts).

 

4. At this point, I'm a blank. I don't know how the the backing plate is attached to the valve cover - screws, bolts, or what. How do the backing plates come off?

They just slide right off after you remove the distributor bolts.

6. Clean backing plate and valve cover surface. Apply Permatex to both sides of new gasket, attach it to backing plate and reinstall backing plate.

I wouldn't do that. I work white grease into the gaskets and on the surface. The gaskets can be removed and replaced without damage.

5. Replace the seal. Again a blank. Is it pressed in or what?

It should come out with the transition housing. It pushes out of the housing with gentle force. Be aware there is a correct rotation of the gasket (indicated by very small ridges on the gasket I.D. slanting opposite the distributor rotation - to push oil back toward the cam).

7. Again a blank. Don't know what the thin cork gaskets are for???

Are they the same as the other gaskets? If so you might use the standard gasket between the transistion ond the head, and the cork between the transistion and the distributor to keep out dust. You may have others weigh in on this comment.

What's the worst that could happen?

Missing the timing. But it sounds like you're being very careful so go for it!

 

Whoops. Didn't see the pix. Ignore #7.

 

Just fixed a very stubborn distr leak.

Personally, I don't think silicone is the best for this application. Hylomar, as someone mentioned above, is better IMHO, as it's non-hardening.

Altho I certainly won't protest replacing everything, you can usually figure out which is the guilty part. When you pull off the distr cap, see if there is oil in there. If so, either the shaft o-ring or the cam seal is having a major gusher, as oil should drain out before getting this far. After pulling the distr itself, look carefully inside. If it's dry, it's the gasket behind the plate. If wet, you can usually figure out by inspection whether the o-ring or the seal is the culprit.

In my case, it was mostly the gasket. A new gasket coated in Hylomar did the trick. This had been a problem off and on since the car was new, so the repair speaks well for Hylomar.