first thing to do is get the check engine light codes canned (Autozone will do it or lend a code reader). Vibrations at low revs can be caused by misfires or motor mount issues (a visual inspection requires one person watching the motor movements while a driver revs the engine and puts the car in/out of gear etc). Shifting issues can be engine ignition or vaccuum leaks or dirty transmission fluid (do a dip stick check to see if the transmission fluid is black and smells burnt). Now to the real concern - metal in the oil. you need to have a tech drop the oil pan and look around to see how much is there before it clogs the oil pump pick up and ruins the engine for good. Usually metal bits suggest a rod or crank case bearing issue. Not sure how they associate metal in the oil to leaks - leaking oil usually is caused by a clogged PCV system which builds up oil pressure and pushes out seals. Not enough to know if the engine is toast or not but the metal in the oil is the most distressing news. Did you have a mechanic do some independent inspection work - it would be worth paying $100 for an hour of diagnostics. Note used engines are easy to come by. Figure 500-750 for a used engine plus 10-12 hours of shop time and you'd be looking in the $2000-$2500 range to replace the engine.