Oil line leak behind dash

try changing the line and using some plumbers thread tape on the joints

I have seen replacement lines on ebay in the uk, burtons may even have them.  I replaced mine, but have determined that it is the actual guage itself that an inner seal is stuffed.  I have left it disconnected and mounted an after market gauge under the dash.

whooligan

The dash may be cracked where it screws into the back (common problem) as people try to rip them out without disconnecting them properly. If this is the case, you'll never stop it leaking as they leak inside the unit. Had to replace two dashes in my RS.
Change the hose and if this doesn't solve the issue, start searching for a better dash.

And speaking of replacing dashes, or more to the point, parts thereof, are spare gauges available from anywhere, or is it a case of repairing what you've got?  I think I need a new fuel gauge you see, and it would be a shame to deny someone a complete dash for the sake of one gauge.
 
P.S.  Sorry if I've hijacked the thread.