Oil leak out of the speedo cable mounting adapter on the tranny

Jacking it up from the back is probably the best so the fluid will run forward. Most I've seen leak from the inner seal not the outer o-ring but it could be either. You'll have to determine which is leaking and aquire the approiate seal/seals from your local auto supply or mopar dealer. Then it's best to first get a drain pan and clean everything first with a can of brake cleaner (may take a couple cans if it's really grimey). If it's the outer seal do like Mike said. If it's the inner seal you may be able to get it without removing the speedometer pinion gear carrier but most likey you'll have to remove it cause it sounds like your exhaust is probably going to be in the way. Remove the carrier and you'll find a little round metal ring holding the inner seal in. You'll need a seal pick to get it out. Remove it and replace the seal. Don't forget to lube the seal up with some lithium grease. and reassemble in reverse order.