Does the flasher (blinker) sound degrade after 40 + years? Anyway to upgrade to a louder sound?

Yes. But for me the odd thing is so has everything else decreased in volume. Especially soft voices at meetings. Oh, you mean the flasher sound itself? The best way to find out would be to buy a replacement. For my TR6 which is not so good at cancelling the turn signal I wired a couple of LEDs in line of sight to supplement the weak dash light because I didn’t hear the flasher. I used actual LED as parts, not cobs or anything really auto oriented. Would think others have the same issue and could b e of more help

I've used these on loud hot rods...

Loud flasher

Or you can make your own...

make your own

I echo the earlier "meeting" comment (not to make a pun). Otherwise, I haven't seen a drop-off those many of the replacements are much softer (and inconsistent....) than the original Hella relay.

I replaced one when I first got my car and was getting the electrics in order,the old one was slow to flash and made little noise,replacement one was easy to hear and flashed @ the correct speed.
IMO too loud and they are a pain.

EDIT;
Also make sure you are getting a full 12volts to the relay (pin 30),if your switch is a little faulty you may not,I cleaned the contacts in my switch and it made a difference.
Good luck .

Luckily, it's not my hearing. Although I do forget things more often.

So, where is the flasher sound unit located that I need to replace? Is it part of the steering column arm switch?

Thanks for the help!

The flasher is located on top of the fuse panel. The fuse panel needs to be dropped to access the flasher. Disconnect the negative cable from the battery before dropping the panel.