Well it looks like the whole thing is no longer available, but some of the seals are available so you are probably going to have to reseal it.
http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=%2079170&ivar=images/CRUISER/79170/31.png&inbr=1595&bnbr=190&bdesc=REVERSE+LOCK+VALVE+ASSEMBLY+%28IN%2DLINE+ENGINES%29
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