Redfield Scope

[ScotZ]

A good friend of mine is buying a Colt AR-15 with a Redfield scope. There seems to be a problem with the scope. The objective lens was stuck. There was a set screw on the ajustment and even when it was removed it still would not turn. After lubing and messing with it, it finally broke free. Questions are: do you have to loosen/tighten every time you want to make an adjustment and would you calibrate this adjument?

The only markings on the scope are 6x18 Redfield, No model # .

TIA