I’m with Edchris, it doesn’t make much sense to me, it ran fine and then stopped. Can you go through with a little further detail why went wrong ? If any work was done just before that and what has been done so far.
If it was running fine before stopping it’s unlikely to be seized, when you turn...
Is it a saltwater engine ? Could well be salted up inside, I would either remove the exhaust cover and have a look to see what state the water passages are or you could turn the engine upsid ev down and put some salt remover down the tell tale (Wessex marine Proflush or Rydlyme) to see if that...
The tell tale isn’t directly connected to the exhaust, can you post up a picture of the back of the engine with the cowl removed, the thermostat housing should be at the back with a hose running down from there to the tell tale.
It sounds like your dealer has run rings round you to be honest, make sure all your fuel is as low ethanol as possible, clean and fresh, you should have an inline fuel filter which sits on the left rear side just before the fuel pump (I normally swap there for a see through one). Once the carb...