I'm afraid it's impossible to prevent it from further fading. It happens because the paint isn't "strong" enough to withstand the chemical reactions due to UV-light. Modern paint can but the one used back then, can't. The only thing you can do is keep it out of sunlight as much as possible.
49,5 cm center bracket-top seattube. I'm planning on cutting the peeled edges of the decals, clean and lightly sand the frame and spray one or two layers of clearcoat (but first will check if the decals will hold).
I'm afraid it's impossible to prevent it from further fading. It happens because the paint isn't "strong" enough to withstand the chemical reactions due to UV-light. Modern paint can but the one used back then, can't. The only thing you can do is keep it out of sunlight as much as possible.
What size is your Comp?