I'm 32, been training since my teens (2 short low dose test cycles) and have a solid foundation plus ok build at 5'10" 180 lb

A while back I was in a major accident and ended up with infections and lots of downtime which obviously isn't great for keeping in shape.

I'm looking for something to help me bounce back. I don't need gains, just something that will keep the gains I have while doing a lot of cardio. Ideally, it wouldn't suppress immune system, wouldn't dry out joints too much, wouldn't give the bloated look, and no "deca" effect on my man below.

I was thinking primo, but turns out my source can't get it now.... so low dose test? suggestions?

A low dose test cycle is all you really need to help you spare muscle while cutting.
Primo or anavar would be very nice to have in there. However, they are luxuries and are not needed.
If all you are worried about is sparing muscle, and you do not care about making gains, I would recommend an 8 week cycle of test prop.
Weeks 1-8
T. prop 100mg EOD.
At that low a dose, I would think, you would have no problem keeping the muscle you have as long as you do not restrict calories too dramatically in too short a period of time.

thanks for that, I'm also curious how that amount of test will affect immune function and if I should take a quarter of a Arimidex or similar with it?

I do not think that a low dose test cycle would effect your immune system. However, everyone reacts differently.
You do not need an anti-e for a cycle that low dosed. However, since you are cutting you may want to use one anyway.
Arimidex, femera or aromasin will help get rid of any water weight you may be holding from the test. Even though at that does it should be minimal.