Doesn't look great, but appears from the picture to be just surface corrosion - they get chipped of course here because of lifting during servicing, mot etc.
If you detect any weakness in the metal here, you'll need that professionally addressed of course, otherwise you could treat it yourself. I wouldn't leave it.
Ironically I'm currently in my garage fettling just these points on my car as part of the 60K service...mine only had a few spots of surface corroision here, but it's a very fiddly area to deal with and time consuming. You will really need a lift of some sort to get the access you need to deal with this. It's the usual remedy though, degrease (I suggest marine degreaser), grind it out ( a cordless dremmel is very useful), treat seam areas where you may not be able to get all rust out with a treatment (I use FE123 from
www.rust.co.uk), apply a good chassis paint (I use two pack mastic from
www.rust.co.uk, but lots of people recommend POR15), apply protector where necessary (I use BiltHammer seam sealer), prime + top coat, then apply some waxoyl or heavier product if you prefer (I use BiltHammer s50 wax mainly).
Despite our vehicles being galvanised it is evident now they are around 20 years old that the protection in some areas will be needing attention. On my vehicle I see small surface corroision points around spot welds that have been exposed on the underside of the chassis where presumably the galvanic cover is poor and similarly on seams where again, the galvanic protection will never have been thick. This is one of the main reasons why I bought myself a lift last year (basic MR1 lifting ramps) because it's long and tedious work to treat this, that would cost a fortune in a garage and I'm keen to make sure it's a very thorough job.
Not wanting to worry you further...but the worst position I am aware of on these cars are the rear chassis legs...do a google search, but make sure your sitting down for the images. if you are getting any work done in this area, I would strongly suggest this area is checked and dealt with - Porsche unfortunately attached the two small plates in the rear wings to the primed body, so there is an area where these attach to the body that is a seat for corrosion to develop. I was fortunate, mine was only mild surface corrosion which I've treated this winter, but some of the worst case pictures are pretty terrifying.
All the best
Andrew
