Currently the Winchester line of air rifles is sold through Daisy air gun company. I suggest you start with them. See if they have a schematic that you can download. Or another idea is to contact an airgun repair shop (There are several independent repair shops that make a living repairing older air guns.) You can search the web for "airgun repair" or see the links below.
The Winchester model 425 was made for Winchester by "Meyer & Grammelspacher" of Germany. The value is determined by the condition of the rifle. without any information about the condition of the pellet rifle, no estimate of value can be determined.
Cal .177
This is a .177 pellet rifle.
It was made sometime between 1965 -1974
A Winchester Model 427 pellet gun in 22 cal shoots at speeds of between 400 and 600 feet per second. The actual velocity varies based on the number of pumps used and the distance to the target.
this particular item is a .22 cal. pellet gun
Please state the condition of the rifle so an estimate of value can be given.
At present, Daisy air gun co distributes and services Winchester air rifles. From 1969 to 1975 Winchester imported eight different models from Meyer & Grammelspacher in Germany. Yours is one of them. It's a Diana model 27.
Numrich Gun Parts Corp would be your best bet in finding a bolt for your Winchester rifle.
25-100 USD
from 1969 to 1975 Winchester imported eight different model Rifles and two guns from Germany. The model, condition and age determine the value. Please repost your question with the model number, and condition for an estimated value.
It was rated at 480 FPS (More like 450 FPS in real life) in 1974