This is all a matter of opinion. So I suggest you watch the video, See the link below.
Gamo's ( Air Guns/Rifles ) are made in Spain. If you want to see their home page click on the link below.
Gamo offers instruction manuals for all their rifles. That include correct aiming with the sights. See the link below
Both companies make fine air rifles. Your question is too general. It's like asking which is better Honda or Toyota without comparing two specific models. Crosman is a larger company and makes air rifles in all categories from inexpensive to costly. Gamo is a smaller company and makes air rifles in the medium to costly range. So trying to say one is better than the other is not a fair comparison. They both make fine air rifles. Now if you had two specific models then you could make a comparison.
Gamo is a manufacturer and retailer of air rifles. They also make and sell a variety of air rifle ammunition and accessories, such as targets and magazines.
Start with the Gamo home page "Gamousa" customer service contact. Or see the link below for shops that repair air rifles.
This is like asking, "IS Ford Better than Chevy?" It all depends on who you ask. I own rifles made by both manufactures and have no preference. It all up to the user. Things I look for in a rifle are how well it is made. I prefer wood over plastic. I like Metal parts. In the last few years I find more and more plastic creeping into the components. Like the Trigger guard. Gamo is known for having a sloppy trigger. But Diana has had some problems. So I suggest reading the reviews on (See the link Below) to see what other people say about the rifles before you purchase one. Also be aware that some models have been discontinued like the Gamo Hunter extreme 1250. It's a fine rifle but no longer made.
If you disassembled it you may want to contact Gamo directly and see if they can help you with a diagram. Call 954-581-5822 Gamo Customer Service. Unlike Crosman who post schematics for all their guns and rifles, Gamo and Daisy does not. Your next best shot is to check the web for an "Air gun repair" shop and send it to them for assembly and repair.
Gamo made a Viper Express Shotgun not a Whisper Express shotgun. They do make a line of Whisper rifles but none of them are shotguns. In fact the Viper shotgun has been discontinued.
Gamo makes a dozen different rifles and pistol's. I find then to be of Very Good quality. I personally prefer the Nitro piston models over Spring. The new Dynamax (PCP) looks promising but expensive.
Get the Silent Stalker, it is far superior in quality. The IGT system is much better.
Usually it stands for "Safety." When activated it keeps the trigger in a safe fire mode.
To get an estimate of value you will need to supply more information. Is this and El Gamo made for Daisy airgun Model 126? is this a El Gamo 126 Super Match? Or is it just one of the 30 different rifles made by Gamo? What is the condition of the rifle? Is it working? What is the model number? Giving me the serial number is no help. Re-post your question with more information and I will try to answer your question