As a general rule the compression ring on the pump slide has become dry and is not sealing properly. A drop of 3in1 oil or similar sewing machine oil on the felt washer or on the rubber ring seal will solve the problem.
Take it to a authorized repair center
Currently there are 3 in production. Daisy Avanti 717, Powerline 008 and the 617x. Crosman, Benjamin and Gamo make a larger selection of pellet pistols.
Daisy Model 717 slide lever pneumatic action. 360 FPS made between 1981-96. $190 to $221 In Like New condition. Blue book of airguns 9th edition
you can start by searching the web for "Airgun Repair' or see the link below.
717 is divisible by: 1, 3, 239, 717.
The factors of 717 are: 1, 3, 239, and 717.The prime factors of 717 are: 3 and 239.
717 as an percent = 71700%
1 x 717, 3 x 239 = 717
720
717 / 3 = 239
717 = DCCXVII
10% of 717 = 71.7