Is that behind the main pulley? And what about cleaning all that deposit? the alternator etc. Steam? will steam damage anything?
yes, it's behind the main pulley at the end of the crankshaft. the seal goes into the timing chain cover. like he ^ said use a gunk removal spray or solution, soak it for a while then spray again and use a brush (paint brush) to soften all the cr#p there - you might have to do it a couple of times. take the dist cap and wires off as well as the intake pipe coming from the air box (take the airbox out too as a matter of fact). Tape ziploc bags over the distributor and throttle body and if you're concerned about the PCM might want to take that off too and take plastic/ziploc bags over the connectors. You should be fine power washing it at this point but watch the spray so you don't force water in the connectors, engine etc (plug the breather tube on the valve cover as well).
I'm not sure how well your alternator will survive, once you fix it you might want to just buy a second hand replacement just in case (stock ones go fairly cheap or you can upgrade and hit 2 birds with 1 stone).