Im just a little concerned about cutting new threads in to aluminum - then putting another SS plug or bolt into it. Just really hesitant overall due to the cost of something goes wrong with a Volvo Penta drive.
Well ya gotta do something !
And everything involves machining that hole . The stainless/aluminium thing doesnt really matter as the sealing washer will stop any water getting in to that union and there will be oil on the inside of the seal where the threads are.
Use only sharp drills and taps , even if you buy 2 new drills ( drill the hole to tapping size in 2 stages ). You have to figure out away to hold the drill bits, easiest is to grind a couple of flats on the drill shank end and hold it in the tap holder.
An assistant is very helpful in assuring drill is at right angles(90⁰) ,get them to hold a square and eyeball the action while you turn the drill ......same deal for the tap .
If you took that housing to an engineers shop this is pretty much what they would do.
End of the day its a fill hole not a main bearing stud hole and if you #uck up the 10mm hole theres alway 12mm or 7/16, 1/2 inch and them holes are to blimmin small anyhow .
These types of screws are ideal ( couldnt find an image of a 10mm one ), the o ring has a bit of "give" . Dont over tighten . Peeps tend to think of the damage if it does come out on the hop , and ya aint gunna know till she chunders.......so they lean on that screw extra hard .....dont. 6 f/lb is plenty
