The problem with using an older, possibly suspect lens for your first LF shooting is you have nothing to compare it to. You may use the lens and think it is totally acceptable compared to previous experience with other formats, yet put up against a newer or more pristine older lens it will be lacking in quality.
If you know any other LF shooters in your area, borrow a lens that is of known quality, regardless of its age. This would show you any major defects in your lens.
If the lens does not produce the quality your seek, but has a good consistent shutter, I would purchase another Xenar maybe from Ebay with a gaurantee and keep the old one. You never have enough good shutters. Other lenses in that price range are 135mm Optars and the 127mm Kodak Ektars.