88 Corolla All-Trac brake problem

Im having a braking problem with my 1988 Toyota Corolla All-trac. Pretty much I have no brakes… It started a couple of weeks ago when I was at a traffic light. While I sat there the brake peddle slowly started to go down and the car crept forward. I had to mash the peddle down to stopme car. I checked the brake fluid and it was full and I checked checked the brake pads and shoes and thoses were good too. I am not really mechanically inclined so I asked around and was told by various people that it could be either the master brake cylinder or the power brake booster. I checked the vacuum on the power brake booster and that seemed fine.

Is there any way for me to figure out which is which without replacing them?

You say the brake pedal slowly goes to the floor? To get it back to normal, do you have to pump it? If so, you may have a bad master cylinder. Basically the fluid blows by seals and the plunger is not being effective.
Since you’re by your admission not mechanically inclined, get that checked very soon. That can cause your car to not stop one day.

Since you are not mechanically inclined you are not going to fix it yourself. Just take your car to a mechanic, preferably a local independent, and describe your symptoms.
If you don;t hear a hissing noise when you step on the pedal, it is more likely the master cylinder than the booster.

If the booster was bad, the pedal would not go to the floor, in fact it would come up and be very hard to hold down or stop the car. If the fluid is not going down, you need a new master cylinder. You need a special tool to mate the master cylinder to the power brake booster so you will probably have to find a good brake shop for this one.