1996 Express 4d55 non turbo

Driving to work this morning up a slight hill, then all the sudden bang! i lost power dropped down a gear and just made the hill. Then i rolled down the hill and found a park.

Car was still running so i thought is was the exhaust which a bit noisy anyway. stopped it and it started again so i figured it wasn't terminal.

Rang a mechanic and he said exhaust manifolds are common problems on these. So i got one took the old one off and it was fine????????? Had a look around the engine and it appears the front Plastic cover had no bolts in it So the crank etc were visible. Also there was a piece missing at the front between the exhaust manifold and plastic cover.

Firstly Plastic WTF????????

Secondly does it sound terminal?? Or do u think fixing trhe cover will make it right.

There was slight oil leek under car which look like it came front of engine, manifold was had no oil inside it but it wouldn't start this arvo. There is not a single nut and bolt holding the cover on.

Any thoughts??????