Two things... P0135 code, and Oil in the airfilter box..

[Boozshey]

So I got a code pulled today. It had been there since I bought the car. No biggy. It's a P0135 O2 sensor problem. Well they wanted $70+ for one and looking around they are all about the same price. Except in the 94 1L is only $25...

What are my options when it comes to the parts I know a lot are interchangeable but I am new to these so any help would be great.

Next thing is I notice they have the air breather from the cam covers going into the air box. Well there is oil in the airbox now. What is the normal fix for this?

All help and patients appreciated...