Am in the process of cleaning the 'black' whatever off the wood deck and want to recoat it with something that will still show the wood color AND last for more than a few months, like some of the 'wood preservatives'
Any auggestions would be greatly appreciated

Cabot's Aussy Timber Oil from Lowes

Any clear or semi transparent stain will last the least amount of time.

As indicated, stains tend not to last long. Cabot's products are highly rated.

Cetol by Sikkens is the best product that we have found. It is pretty expensive, but is considered to be one of the best exterior products on the market. It comes in many wood stain colors. You need to make sure that you use something to eradicate mold spores no matter what you use. Paint stores carry such products. I think one is called TSP.