98 Bonnieville / 3800 Engine Problems

Hello
I wanted to see if there were any Pontiac mechanic's or people whom work alot on these engines. I have a few questions.
First, let me start by telling you about my car, it's a 98 Pontiac
Bonneville which I purchased used last November when it was a lease return with only 39,800 miles on it.
Well, it's been running fine till in Sept when on the way to work (following a weekend trip of over 600 miles with no problems or sign of problems), the car "check engine" light came on and the engine started running very roughly.
I thought I'd see if I could get it on the work about 4 miles. Well, it didn't make it but about another 1/4 mile and stopped and wouldn't start. I left it there and luckly a coworker driving by stopped and gave me a ride on to work.
After work, I checked on the car and found that it did appear that the coolant level had gone down. The car would not turn over. So, I had it towed to a shop the next day where they said the upper and lower intake manifold had failed. $1200 latter, I got the car back running, but it still had a strange noise (tapping sound like a lifter with a blockage or something, more noticeable at certain RPM ranges).
It now appears that the engine is making metal in the oil since after my wife had it quite running (stalled and acting like it wasn't getting enough gas), I got it home and parked it and it's been sitting since I had this happen shortly before I got laid off.
I wanted some advice on how hard or expensive my various options for fixing this should be. The mechanic who did the intake job thought if I could get a used engine, it would cost about $1,200 in labor to "swap them out".
GM says there's no recall or anything they will do about this, which is poor support for a couple year old car with only about 52,000 miles. On the internet, i've gotten some quotes for used engines from about $500 to about $1200 shipped.
If I was to go with a used engine.. What all should I check on it before it gets installed in my car. What parts should be replaced while it's still out of the car (I.E. new oil pump, timing chain, etc)
How are rebuilt engines from various auto parts dealers like Pep boys, Autozone, etc.. Are they reliable and long lasting?
Is there a chance that my existing engine could just be repaired and last a number of years with only bearing changes on the crank?
I trust the 3800 engines pretty well. I've had 3800's in my last 3 cars and in my 95 Transport which now has over 148,000 miles on it. So, I know the engines can last. But, I want to be sure it will last if I spend the $$ to repair this car.
If your experienced on repairing or troubleshooting, please e-mail me your recommendations on how to approach this the cheapest, but most relable way to fix it.
Thanks
Mike Harvey mhavey5mcp(remove spamguard)@yahoo.com
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Mike a couple of issues here, the shop should have drained the oil and looked closely for debris and /or coolant in the oil. then pull the pan and see if the bearings were affected by this. We warn the customkers that failing to do this risks severe engine damage, if it isn't already too late. At this point I would say it probably"spun" or scored some bearings and the lower end is done. Certainly a used engine is the cheapest route. Make sure it is not sludged up or shows lack of maintenence, also might want to do the intake gaskets before installing. Timing chains are not an issue with this engine.
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