contact consumer affairs and discuss it with them, see what they recommend.
the dealer has first option to fix the issue, if you are polite with them they might fix it properly.
buying a skyline will always cost you money, so if you wanted something that will not be a constant expense you bought the wrong car. For that matter any 20 year old car will be the same.....
unfortunately I think you will be in for a long painful process with this dealer, so might be better to try get a refund on the warranty and go it yourself.
any car of this variety should be thoroughly checked out before purchase, even if from a dealer as they really don't know anything about it and only do a quick once over and tidy up so they can flog it off..