I bought the car 2 weeks ago on impulse. Last tune up according to records 01/22/09 with Cat replacement. O2 sensor replaced in 2004. Can it fail again?

I am not sure about spark plugs, bought them (Bosch 7927) from auto zone and checked on Bosch website that they fit my car.

Distributor cap & rotor R&R 2005; air filter just replaced last week after purchase.

What troubles me is that on my 1996 E320 at least I can plug an OBDII scanner in and get some clues, but pre-1992 cars don't have that nice feature.

__________________
1996 E320 since 1/16/08, 171K miles as of Feb 2011

---------------------------------------------------------
1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE