OKAY. Lets start with your question. The Silver Streak, There were two different models of the Silver Streak pellet RIFLE. First there was the model Silver Streak "C" that was made from 1949 to 1990. Then there was the Silver Streak "C9" from 1995 to 1997. Both were made under the "Sheridan" Brand Name not Crosman.
If you want an estimate of value then you will have to provide me with the model number "C" or "C9" and the current condition of the rifle. Give it some sort of rating like Poor, Fair, Good, Very Good or Excellent Condition. Then I can give you an estimate of value.
Without this basic information it is not possible to answer you.
What condition is it in. That determines the value
If it is a "C9 silver Streak" it would be worth around $140. If it is a "C Silver Streak" it would be worth around $235
What model is it. How old is it, what condition is it in, is it still working?
This is for the Sliver Streak not the C9 silver streak. In good condition it is worth between $85- $105
It's worth around $130 IN WORKING Condition. Also check the ( link below ) for shops that repair older air guns. Today Crosman air gun company owns the Sheridan name and products.
This is possibly the most frustrating airguns to nail down as to the exact model. First of all let me explain. Sheridan was a standalone company. In 1977 Benjamin purchased Sheridan. Some guns were called Benjamin/Sheridan, in 1992 Crosman purchased Benjamin and Sheridan. They decided to call the .177 and .22 caliber rifles "Benjamin" and the .20 caliber rifle "Sheridan." But for awhile they were called "Benjamin/Sheridan." So now we have the models C, C9, CB9, C9PB, Along with Blue Streak and Silver Streak. Not to be confused with the Crosman/Benjamin "Super Streak." (Confused enough) Okay here is what I think your value is according to the Bluebook of airguns 9th edition. in very good condition it is worth between $105 to $135
It would be worth around $65 in Excellent shape.
In excellent working condition it would be worth between $75-$95. Like New it is worth around $110. W/O scope.
I have absolutely no information on a Crosman model 143. Are you sure it isn't a model 140 or model 147. I even searched the net and can not find anything on a model 143.
This model was made between 1966 to 1983 in fair condition it is worth between $45 - $70
It would be worth between $65 - $75. Add 20% for the box
Crosman made the pellet and bb guns for Sears starting in the 50's I am not sure when they stopped, I think probably sometime during the 70's. Sounds like you have a variation of the pumpmaster Crosman, so best guess, is if its older, anywhere from $50-$100. You can probably check on Crosman Forums, and get a better suited answer there. Hope it helps.