I own a 1987 Mercury 115HP in-line six-cylinder 2-stroke outboard (have owned it since new). I change spark plugs every two years just to keep it running strong. I have now found out that NGK 2622 BUHW spark plugs that I have run all these years are no longer available and would like to find an equivalent (or better) spark plug. Can anyone suggest a spark plug that is a good cross-reference to the NGK 2622 BUHW?