I own a 1992 240 with 272,000 miles.

I had not driven it for about a month or so, and when I did, the check engine light came on.

I took it to a mechanic and he reported two fault codes; a bad oxygen sensor and pinholes in an intake boot.

I can have the mechanic replace the O2 sensor for $360 in parts (for a Bosch) or I can get one myself for $200 including shipping (a Bosch) and install it myself.

Two questions.
1. If I buy the Bosch O2 sensor myself, what are the odds it's specifically the right one and the 'check engine' light will go out?
2. If I get one myself, I may not get around to installing it for a few weeks. Am I doing my car any harm by driving it with a bad O2 sensor? (car still seems to run okay).

Thanks.