If you are getting P0300 series misfire codes, your coils or plugs are most likely the issue. I'd start there. And if this is the case with the codes, the Durametric is not going to tell you any more; you need to start doing close up diagnostics to ID the source.

Totally agree....time to get your hands dirty

Thanks for the info, JFP! Last summer I had a freak misfire episode (the CEL was flashing and engine clearly missing when it was happening, but fixed itself after shutting the car off, waiting a couple minutes, and restarting) that ended up being a P0303 - "Cylinder 3 misfire detected", so your advice seems like it should also be applicable in my case.

Looking under the car closely recently, I noticed there was evidence of a very a slight oil leak in middle cylinder on right (passenger) side. I wonder if that's cylinder #3. I have a set of new plugs ready to go, as well as new o-rings for the spark plug tubes. I suppose I should inspect the coils for cracks (especially whichever one is #3).

It's a 2001 boxster base 2.7 with a bit over 100k miles on it.

Hey Jakeru! Porsche cylinders are numbered in order from front (closest to passenger compartment) to back. Bank #1 cylinders on pass side are 1,2 & 3. Bank 2, driver side are 4,5 & 6. so middle cylinder leaking on your car is #2.

Thanks.
Is it likely that 3 or 4 would go faulty all together?
Is there any test I can do before buying replacements and just swapping out parts?

Yes. Do the proper diagnostic checks, scan the car, check the coil pack connections, check the coils for cracks, etc.

I've now got the Durametric - and how right you are. It is showing a misfire code and nothing more. Guess I will now be getting my hands dirty and starting with the plugs and coils.

I might regret getting the Durametric now that I see the ignition range readings. From my limited understanding of them the over revs look very high!
Range 1 33785 / 2232 Hours
Range 2 145 / 372 Hours

Total Hours 2257

I assume range 2 at 145 is not good but at least it was a long long time back - is that correct? (Current mileage is 61000 by the way).

Is there anything in particular I should now check with the Durametric (other than fault codes)?

Bear in mind that Range 1 is hitting the rev limiter
Range 2 is over redline

Happy to report that after replacing 6 cracked coil packs and with 6 new plugs and a short test drive the car is running beautifully. A very satisfying bit of DIY car work.

Perhaps it was unnecessary buying the Durametric, so any advice on what else I could usefully learn from it would be appreciated.

Next on my list of jobs is replacing the brake fluid.

That is a fairly small number of Range 2 over-rev's. Nothing to worry about.