the oil leake mostly come sudden from a broken sealingring on the metalpipes that are covering the valverods. you can fix that yourself with a book. there are not many engines you can swap,.. because of the air cooled engine. its a lot of work to put the waterhoses and the radiator in the front and to change electric for your instruments.
in your case ,.. if affordable,.. i would think about rebuilding the engine what is not really a big deal. this engines are very simple and with some right informations and a book you can do it yourself. the 2.0L should be a "CU" block that is mostly identical with the porsche 914. what means for a rebuild that you can directly upgrade the engine with a 914 injection cam and 9,25 pistons. for the upper part you can after this easyli switch on weber carbs or 40s from delorto. the best thing would be to search a scrabyard for an old golf gti with injection cause its pretty easy to do this swap on the intake. after that you will not only have a better running engine,.. you should also gain arround 40 horses.
hope i could help
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