I was handed down a 98 S70. I just discovered this brown [cappuccino] gunk on the dipstick housing (not in or on the filler cap). I live in Las Vegas and the Temps lately have been well over 100F. Had an oil change 2 months ago. I drive to work 22 miles. Not much rain happens, but we have gotten some in between that last oil change and now.

I've seen some of the replies to this, and am mystified how I could have moisture build-up. ??? What to remedy?

 

Welcome to the forum Celtson

The brown gunk is likely caused not from external conditions but a problem with your PCV system. As the hoses age they can get soft and spongy and break down internally clogging the passage or brittle and split causing vacuum leaks. In both cases the engine isn't able to pull the air and gasses out of the crankcase and back into the intake to burn them. You start to get moisture built up inside the engine from the lack of air circulation that's supposed to bring in fresh air and pull out the bad stuff.

 

This is probably the best, most simple explanation for this. Time to replace the PCV. I seriously doubt it's the head gasket.

 

I bought the whole kit before I knew what was (wasn't) inside that black box. I figured it was some sort of metering system that could clog up like a the regular little PCVs on most cars when all the black box does is just offer a place to allow the oil to drop out of the air flow.

With really poor maintenance that box can plug up but usually if you're having a problem with condensation on the dipstick or under the oil fill cover it's from a clogged or split vacuum hose and replacing all the hoses is good enough. In extreme cases the passage inside the oil pan that connects to one of the black boxes ports can clog. If it is, nothing is going to help until that port is opened up.

If you're going to pull the box best to do it shortly before you need to do an oil chance as it's sometimes necessary to rod out those two ports for the black box and it may involve pushing some cruddy material into the engine block if you can't fish it out.

That way you complete the job, run and or drive some and then change oil and filter so you get anything out that was dislodged during the procedure.

Here is Robert's video on checking the system out.
https://www.youtube.com/watch?v=FIRoc0VxLd4

 

Good to know for future reference.