I'm taking my mint 76 914 to a race friend specialist Monday. The brake pedal lately seems to go too far before braking effect. The master cylinder reservoir shows no sign of loss of fluid, nor do I see any sign of brake fluid on the garage floor. The brake pads seem like they have life left. I don't drive it a lot, and it has been ages since I think the pads were replaced, but again, they look ok. I have never changed the brake fluid, figuring if it ain't broke...
Would anyone hazard a guess based on these facts on where we might look first?

Sounds like air in the system. Or faulty master cylinder.

Brake fluid picks up water just sitting there, you should change it every few years. Sounds like you should bleed them anyway, it could be seal going in the master cylinder, but bleeding would be my first move.

I'd adjust rear caliper "venting" and then flush hydraulics...

E-brake adjustment at the caliper?

The Allens under the caps set caliper piston depth.

The only cars I've seen this adjustment style is the 914 and Miatas (no shit!).

It's stupid and unnecessary IMO but pedal height is seriously tied to this adjustment in both cars.

Both cars take 1/2 the suggested clearance to work properly.

Always flush your brake fluid every other year

Let's see what your race friend says.

But, maybe you need a new master cylinder. And if/when you replace the MC, flush out the old fluid well. Going forward, put flushing the brake fluid on your annual maintenance schedule.

Most likely will need a new master cylinder
Directly caused by contaminated brake fluid not being flushed

Once you have completed the job of replacing an MC
You will understand how much easier it is to bleed your brakes as maintenance, over doing this job again

Rear calipers with an integral parking brake require an adjustment mechanism to set the proper venting clearance in order to meet FMVSS 135 hill hold requirements.

Many vehicles exotic as Ferraris and as affordable as the Toyota MR2 and many 80s/90s Honda’s used integral parking brake rear calipers that required venting clearance adjustment. They tend to only be used on relatively light weight vehicles due to their limited hill hold efficiency.

The other common option that replaces a caliper with an integral parking brake is to use a drum-in-hat (DIH) parking brake in addition to the rear caliper (i.e. 911 style). This is more expensive, and heavier. I’m sure you can appreciate how much it sucks to service DIH parking brakes once the hat has either worn deeply or has enough of a rust ring to prevent the drum from being removed.

Adjustable rear calipers are neither stupid or unnecessary.

Various types of rear caliper adjustment:
https://www.hella.com/techworld/us/ti/Brake...mechanism-9219/

My thoughts are that you need to think about preventative maintenance for yourself.

Oil
Fuel
Brake Fluid

Probably in this order. It is vital to also at least exercise the car every few months and the reason is if the fluid has absorbed some water it will or can oxidize the piston bores causing the pistons to stick.

The maintenance period for brake fluid is 2 years. In my Cayman and since I depended on it to stop the car, a very big deal. Later it can be very expensive if you ignore doing it.

The rear venting gap is somewhat of a pain to do but once set, you normally don't set them often if you don't do a lot of driving. That is something if you've never done it before you might need help with.

Suggest you may want to change your mindset and mantra about routine maintenance.

You asked for thoughts.

Rear venting isn't bad once you have pmb rebuild your rear calipers. And as someone mentioned, half what the manual says. My younger son and I have turned bleeding and vent setting into a bonding experience.