Ok guys and gals, here's my issue:

Ride: 1998 z34 3.8l NA
Codes: system to lean, bank 1
Symptoms:
-temp gauge up and down between 100* and normal op temp
-coolant dye around gasket between uim and lim
-coolant dye around egr tube to the intake manifold
-low coolant light every once in awhile, only after sitting 6+ hrs

Backstory:
Last winter my lower radiator hose blew off w/o me knowing, effectivly frying my original engine. Crate motor from AutoZone was installed, new lim, water pump, etc. The uim was not replaced.

So, would it be feasible to assume that the uim has failed and is leaking coolant into my engine? I know what they say about assuming, but it does seem to b a common failure point on these engines. The uim has roughly 190k on it, the rest of the engine has like 20k (if that)

edit: added symptoms

 

That is a good assumption...190K on the UIM gasket is way more than most people get out of them before they start leaking.

Also, just to throw this out there, my sisters car (Toyota Solora) had the same code thrown, "system to lean, bank 1" and it turned out to be a hole in the brake booster.

In your case given the common issue with LIM/ UIM gaskets, i'm sure that the problem.

 

Surprisingly the autoparts store had an oem one in stock, for only $120. I think I will be trying to put it on through the holiday break and see how my car acts after this.

I know that its loosing coolant, and considering this is the only part of the engine that isn't relatively new, I will be starting here.

Keep your fingers crossed that this' the problem and I don't have to tear down the entire heads...