IF it does turn out to be water jacket seals then you have my sympathy
The following thread is quite long but well worth reading
IF you plan on tackling water jacket seals yourself.
https://club8090.co.uk/forum/viewtopic.php?f=37&t=52374" onclick="window.open(this.href);return false;
The potential for an unsuccessful outcome is not to be ignored. This is a BIG job that can go wrong (ask me how I know

) and then you have wasted a lot of time and money only to still be faced with an unusable engine.
Personally, having gone down this route myself, if I had to do it again I would rather buy an Elite re-con
Hopefully it will be summat MUCH simpler (like a core plug etc etc)