The plastic becomes brittle after a while, so just replace it or go with the copper line from NAPA or one of the venders on this site. The piece that fits the gauge is a compression fitting, you will need to replace it or open it back up to accept the new line. Look at the link to Classic Parts above, you will see the end of the brass fitting is a cone, this squeezes the copper line sealing it off. If yours is already clamped down on plastic line, it will be tough to get the new copper line in place. Its best to cut the old line at the gauge and back the fitting out using a small wrench, 1/4" or 5/16". NAPA might have the gauge fitting as well as the line, take the old one with you. The block should have a 1/4" pipe threaded hole, just remove the oil line fitting and install a plug of the same thread.
Joe
