Leak off pipes are 3.2mm inside diameter, 4mm will leak very quickly.
If bolt is tight and alt is loose alt casing is probably fcuked, so even if you fit a new alt it may need need a washer as a spacer to keep it tight.
No spacers on the alternator now and it definitely wants them. Casing has chipped away on one side of the mount, but there's a sleeve in it which seems OK and it charges good, so I'll quick fix, and keep an eye on it.
Will have a good look around for anything that wants careful cleaning after getting soaked in diesel too.
Just finished fitting a new starter when I "discovered" these, so no telling what's next