I have an old franke faucet ff300 which has been working perfectly for 20 years until this week.
The water now comes out of the sprayer as well as the normal faucet hole. When I switch it to sprayer the water in the normal faucet hole lessens but still water comes out. What do you think is wrong and what parts would I need?

Try and see if you can clean the spray button assembly. The thing you push to make the water divert from the faucet to the hand held sprayer. It could just be getting a build-up of lime and debris. If you notice any worn washers, take them to your local harfdware store and match them up. Good luck.