Oil leak pan vs. rear main
 

I have an oil leak looks like from rear of oil pan but not sure if it could be rear main seal leaking. Oil pan bolts and pan wet with oil, leaks even when engine not running. When I look up between back of pan and flywheel, I don't see any obvious oil. So is it only the pan leaking and not rear main? Factory manual says pan can be removed without pulling engine; has anyone done this?

The easiest way to tell the difference is look at the flywheel. If there's not oil slung from the center of the flywheel then chances are good that it's just the pan.

For my 455 I had a leaky rear seal, and the give away was a persistent oil leak that slung all over the inside of the fly wheel dust cover and dripped down through the little drain hole in the bottom. Same idea as 63 bomb stated. Problem solved after replacing seal. Separately, your description seems like it is an oil pan leak. Because of some recent engine work, for the first time I used a BOP Pontiac One-Piece Oil Pan Gasket. Great improvement over the OEM style multi-piece. I also used Pontiac V-8 oil pan reinforcement plates on the back corners for insurance. Not sure if they helped, but those corners can be a nuisance,

Pulling the pan in an F body is no treat, maybe you have an A body?
Gasket & rear seal can be done in the car.
Let's see some photos, where you at?

Yeah, on an F Body the pan gasket is doable but not all that fun. In the car, I have had better luck removing the motor mount bolts and raising the engine just a tad. Not enough to affect anything else, but enough to get some squeeze room. Although some people will not like this, I simply raised the engine a tad with a jack on the balancer. Not sure if I would do this again, but for the situation it caused no problems. Just a thought.

That is the Factory way to remove/replace the pan.
Unbolt mounts and lift from the front.

The Factory Service Tool Kit had a nifty brace/bracket to do this.

I myself took a 12" piece of 4x4 and cut a radius into it on one side and use it under the damper.
You only need to lift it about 2" in an A-Body.

So I was able to remove the oil pan with engine in the car (67 LeMans). I didn't have factory tool to raise engine at balancer, so I made one up by using 4x12x1/4 in steel plate with holes drilled to bolt to balancer and 1x1 square tube from which to lift. I used washers behind the plate to fill void between plate and recessed front of balancer. Had to raise the motor until bell housing bottomed out on firewall (manual says raise 4 1/2 "). Even then pan barely came out.

I think rear main seal is OK as no oil on front of flywheel. Waiting for replacement seal for oil pickup tube then will reinstall cleaned pan. Getting in place with gasket may be challenging as not much clearance. Anyone use sealant on gasket? If so which one?

If there is a question on mating surfaces, which is expected with 50+ YO parts
I always use "Indian Head" Gasket Shellac.
A little goes a long way, so I find a very light/thin coat works best.
I have used this on the Oil Pan, Cam Housing & Acc Housing in the past.

Indian head would be just fine as stated above. If you have a hard time finding that, Permatex Avaition Form a Gasket is very similar and may be easier to find. It's a little Brush cap style liquid sealer. Even though many, many people do it, RTV is not recommended to be used over gasket material as a sealer.