There are 3 versions of the 766 see the link below for the owners manual and parts list.
See the link below it has all the Crosman Owners and Parts manuals online.
Crosman has the parts diagram online. There were 3 different versions. See the link below for the first version. http://www.crosman.com/pdf/manuals/crosman/766/C766-EVP1.pdf
See the link below for a view of the Crosman 766
You mean "Pellets". See the link below
You have blown seals or O-Rings. The rifle was made from 1975 to 1982. Crosman no longer makes parts for this airgun. BUT they offer a service to locate repair shops that repair the rifle. See the link Below. But first consider this. IF the rifle was in working order AND it was in perfect shape it would be worth around $50 to $60. Is it worth repairing? It would cost you almost that much to have it repaired. Today you can purchase a brand new Crosman 2100 ( almost Identical to your old 766 ) for $60 through "Pyramyd air" See the link below. It's up to you.
What condition is it in? You need to give more information about the rifle. It was made between 1975-1982. Without more information it is not possible to give you an estimate of value.
There are three different versions of the 766 but all three load the same. All load through the oval trap door on the pistol grip. See the link below for the Owners Manual
You have two choices. 1. Go to www.crosman.com and click on "download a manual." Find a diagram for your 766 and try to repair it yourself. or. 2. Go to www.crosman.com and click on "find a service center" and locate one near you and have it repaired.
Crosman offers a service to locate shops that repair air guns that are out of warranty. This service is free. See the link below. http://www.crosman.com/cs/service-center
Go to the CROSMAN homepage and click on "find a repair center" it will help you find a repair center that handles your rifle See the related link.
766 ft = 233.5 metres, approx.766 ft = 233.5 metres, approx.766 ft = 233.5 metres, approx.766 ft = 233.5 metres, approx.