(It all depends on what is wrong with it.) I suggest you send it to a repair shop. search the web for "Airgun repair" and locate a shop near you for repairs.
Not meant to be disassembled
There are 4 variations of the Daisy model 99 BB rifle, not gun. Your best bet is to contact Daisy directly. They offer a free service to evaluate Daisy antiques. See the link below.
There are 4 different variations of the Daisy Model 99, starting in 1959 to 1979. Daisy offers a free service to tell you more about your old BB gun. See the link below
I've gone through several air gun catalogues and have been unable to locate a Daisy model 170 bb gun that has ever been made. I did find a Daisy BB gun model 5170 and a BB rifle model 1170 along with a BB rifle model 107 but "NO" model 170. However I suggest you search the web for "Daisy Air gun Repair" or "Air gun repair" and locate someone near you who can help you.
I suggest you go online and do a search for 'Air gun repair." and locate someone who fixed Daisy's.
Daisy offers a service for older BB guns see the link below.
No published sn data.
It was only made in 1967.
This BB rifle was made for Sears by Daisy air gun company. It's really a model 1894 and possibly one of the hardest BB rifles to repair. I suggest you look online for "Daisy air gun repair" and locate a shop near you to have it repaired. There are shops that make a living repairing outdated air guns and rifles.
I suggest Crosman Pellgun oil or RWS pellet gun oil.
Do a search online for "Air Gun repair." There are several independent shops that repair older air guns. SEE the Link Below.
I suggest you go online and do a search for 'Air gun repair." and locate someone who fixed Daisy's.