I have no idea why that engine started like that, but I'm willing to bet your impeller for your water pump has suffered serious damage. As little as 15 seconds is enough to destroy an impeller that's running dry. You might have had a little more time due to the fact you said you ran the engine at the shop.. so the inside housing was wet to start with..... but that only gains you a few extra seconds.
If you want to check the impeller without taking it apart, put the engine in water (tub, lake, river, whatever) and see if it pumps ok. Putting it on muffs isn't an accurate test since the water pressure in the hose provides extra pressure to help force the water through the engine. Look carefully at your tattletail and make sure that it's pumping ok.
Personally, I wouldn't take the chance... $24 for a new impeller is a lot cheaper than $2400 for a replacement engine. Spend the time and money and simply replace it.
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1987 V20 w/1987 150HP Yamaha on a Shoreland'r Trailer
1978 16.5 Airslot w/1996 120HP Force on a Four Winns trailer
1996 V21 w/1993 200HP Mercury on a Shoreline Trailer
All towed by a 5.7L Hemi Durango.
If God didn't have a purpose for us we wouldn't be here, so
Live simply, Love generously, Care deeply, Speak kindly.
(Leave the rest to God)
Silence, in the face of evil, is itself evil. Not to speak is to speak, not to act is to act. God will not hold us guiltless.