Aaahhh ... both the joys and cries of owning an 86 ...
Have to take the up's with the down's - actually, what I've found out is that performance and old cars seldom mix. Mine started to burn oil yesterday after Saturday's run with a couple of Silvia's & Skyline's down Mt Cootha.
Well ... hope that Nulon 'Stop Leak' does the ol' trick otherwise me thinks it's either look for another engine or replace something.
Honestly though, if it costs more than $1k to fix your engine, you might consider an engine swap as I know that I can do that for that price (replacing 4AGE with another one).