Tune up interval advice
 

My last valve adjust / major tuneup was 3 years, 1 month, and 19,000 miles ago. Should I consider a valve adjust at this point, or is it safe to let it ride for awhile? Car is running like a top now. 1986 Carrera, currently at 172k miles. Thanks ...

My service intervals for my 911 are at multiples of 3,000.
every 3,000 - Oil/filter change
every 15,000 - Tune, valve adjust, transmission oil change, air filter, fuel filter etc.

I'd say it's time for a valve adjust at that mileage, but I tend to over-service. Keep in mind that your valves will likely get tighter over time rather than looser, which might not be terribly good.

I do mine about every two years or ~15 000 km on average (about 11 000 miles) and change the oil once a year except on those higher mileage years. However, I like Harry's system.

If you learn to do it yourself, you will likely get a good feeling from the exercise once complete. The first time will take you a day and some frustration until you get the hang of it, and the second time, half that. Subsequent adjustments will probably get even quicker.

The only thing I would add is that for my cars using Synth oils, the interval is 5000 not 3000 miles.
And major services at multiples of 25000 miles.