Here is the link to all of the manuals for Sheridan and Benjamin.
Crosman owns Sheridan and Benjamin
See the link below.
The Sheridan Silver streak air rifle was made from 1949 up to the 1990's after that it became the Blue Streak.
There are 3 versions of the Sheridan Blue Streak. See the link below for the 2nd version. BTW today Crosman owns the Sheridan and Benjamin line of air guns. This link is from Crosman
If you are looking for a diagram. Crossman (Owns Sheridan) has diagrams on-line on their homepage. See the link below and click on "Download a manual." You will also find the parts diagram on the same page as the owners manual.
what condition is the rifle in.
It was made in 1975
The Benjamin or Sheridan pump rifle should never be pumped more than 8 times. See the link below for the owners manual (Crosman owns Benjamin and Sheridan air rifles)
It was made in 1974.
It all depends on age, use, and condition of the rifle. Is it in Poor, Fair, Good, Very good or Excellent condition. Sheridan made 4 different model C series. The C Silver Streak, C9 Silver Streak, CB9 Blue Streak, and C9BP. Which one are you asking about?
Sheridan has been making air rifles since the 40's. Sheridan was purchased by Benjamin air gun co and eventually Benjamin was purchased by Crosman air gun co. All the reference material states that the 20 Cal Blue streak was introduced in 1995 and is still in production. Bluebook of airguns says that there are 4 variations of the Blue streak. It also stated, depending on the version, that value for one in Very Good condition would be around $135 Plus or minus. For the owners manual see the link below.
You did not state the condition of the rifle, so I am going to assume it is in "Good" condition, Not Very Good or fair condition. It would be worth between $85 - $105 add 15% for the Box and Owners Manual. If the rifle is in "Very Good" condition then it would be worth around $130
Sheridan C Sliver streak and CB Blue streak. Nickel or black 19.5 inch barrel Walnut stock. rotating safety. C9 Sliver streak 19.38 inch barrel, rifled brass barrel, nickel finish American hardwood stock. CB9 Blue streak Same as above except Black finish. C9BP Polished brass plating "may" have medallion in the stock All of these are .20 caliber. Crosman airguns owns both Sheridan and Benjamin air rifles and guns. All Sheridan rifles are .20 caliber. All Benjamin rifles are either .177 or .22 caliber but both use the same design and stock. See the link below for the owners manual
Sheridan made several C series rifles. I assume that you are asking about the C Silver Streak. Not the C9 Sliver Streak. In order to give you an estimate I need to know the condition of the rifle. Does it still work? Does it hold air. What condition is it in? All these determine the current value.