Please help diagnose computer trouble

[bimmer525]

Hi All,
I have a 95/525i with 151k miles on it. It been running well for about a year now. The first trouble I had was with the check engine light, which came on last december, I did the usual tests and determined that it was the O2 sensor. I *did not* replace the sensor, and was on a 1000 mile road trip. Early Jan this year, the battery drained, and I had to jumpstart the car (AAA), upon which the CEL reset and didnot light up with average driving in the city.

All of a sudden 4 weeks ago my alternator gave up and we had to put in a new one. After this I immediately went on a 1000 mile RT again with no trouble (but for excessive emission at times). Last week my CEL came on again for the O2 sensor. I took the car to a dealer and got the O2 sensor replaced. On my way back from the dealer the car stalled and the CEL came on again, this time with a 1222 code. I took it back and his initial diagosis was that he might have put a wrong part.

After replacing it once more the CEL again came on (but not stall) and I took it back to the dealer. After 4 days he tells me that the computer (??) is short circuited and it might be the reason the CEL trips. He says it could because of the previous alternator and wants $1.3k to change the computer. The check engine light is still on.

Can you all tell me what should I do and what could be wrong with the car? I know that the car is pretty solid and usually does last a long long time, could someone tell me how much long can I expect it to run?

Thanks in advance all.