I really hope I didnt buy a lemon... I just bought a 93 fd and I was changing the oil yesterday to find this yellowish residue in the oil cap and in the oil filler well. My buddy who goes to UTI told me that it is most likely coolant leaking into the engine somewhere or the intake manifold and then collecting in the pan and recirculating into the engine. He asked one of the technicians at UTI today and told him that the only thing to do is replace the entire rotary engine because there is most likely a crack in the rotary's aluminum seals. Is what he is saying true.. Is there a chance I can rip apart the motor myself and find the leak and fix it? Any help would be great!

 

How much residue are we talking about?
Does the motor run good? How many miles?
Is there a sweet smell in the exhaust (don't snort to much smelling)
Does the radiator fluid drop over time?

Lets start with a much more simple approach to this question.

Try pressure testing the cooling system with a pressure tester and see if it leaks down.
Put about 8 - 10 psi on it and leave it set for about 30 to 60 minutes see if it looses pressure.
If it looses a small amount check every hose connection (many) and retest again.

True if you are internally leaking it is a major problem, however ripping into a rotary is not for the faint of heart and not for the average weekend mechanic to try if the goal is to get the car on the road again.

many times here in Wisconsin when the weather shifts from cold to warm and the cars have been in storage there will be milkshake looking residue in the filler cap when you look. After warming up the motor and changing oil and wiping out the cap it will not return until the next year.

 

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/lemon-help-please-650652/