Sorry, Capt Camel, I missed your OP. Don't know how I did because I have been sailing this desk 12 hours daily since 11 March with nothing to do but surf the net & haunt CF. The things one does for cruising kitty transfusions.
anyhow back to OP. So you got the zincs out. How many were there? On the Yanmar 3GM30
there are three - one at the rear and two on the left side looking from the front. One of these is directly underneath the secondary fuel filter
which makes it a real bastard to remove. Why oh why do engine
makers do that sort of thing.
FYI I check my zincs every six months. They should be replaced if they are over one third lost
. Note down in your engine maintenance
book (everyone should have one of these babies to keep a tag on oil
use and your preventative maintenance
schedule) the state of decay and the date of inspection
of each zinc so that if they suddenly start to decay quicker you will know right away and then can search for the electrolytic reason.