What's that noise?
 

Greetings,
My 2001 Boxster S, 78,000mi, has started making a loud, high pitched squeal after it warms up. An online 'expert' suggested I loosen the oil filler cap while this noise is present and see if that cures the problem. It did. My understanding is that the AOS is defective and is pulling air through the front seal. Here's my question. Will replacing the AOS cure the problem or is there now a need to replace the foward main seal as well. All advice is greatly appreciated.

Jack

I'd replace the AOS first and keep an eye on the oil seal to see if it is leaking. If so, then you'll need to replace it as well. Is sounds as if it just started doing this, so you may have caught it in time where you only need to replace the AOS.