Marlin
they were only made in 1965
Depending on condition, about the same as any Marlin 70 rifle.
1988.
50-100 USD
50-135 USD
I have one and it's a 22 caliber.
Early firearms in .22 caliber were not required to have a serial number. Your Marlin 81 falls into this time frame.
The value of that gun would be about anywhere from 150 to 200.
The Sears Model 42DL .22 caliber rifle was manufactured by Marlin Firearms, their Model 80. Check with Marlin for parts availability.
Numrich gun parts, look under Marlin/Glenfield parts list
Made by Marlin, it's a version of the Marlin Model 81. sales@countrygunsmith.net