Have you used Don Moyer's website, parts, and forums at moyermarine.com?
Have you maintained a diesel before? (They don't quite run themselves.)
You're $4k frustrated with that A4? (The difference between the worst-case scenario, a total A4 rebuild, and a diesel repowering).
Just asking. If your answers are yes to all three then you are well-qualified to make the statement "spending too much time on the A4," and, since everyone knows that time = money, you are also spending too much money on the A4.
(My answers are yes, yes, and hell no--to me the only problem with the A4 is the relatively short range of gas engines vs. diesel, but I haven't tested that limit in years.)