[87supraturbo]

I just got a 87 turbo 5 spd the other day that is in very nice condition although rather high miles (160 000) but as i was just checking things out under the hood today i opened up the rad cap and there was kind of rusty water on the inside which leads me to beleive there is maybe a leak where moisture is getting in somewhere? any suggestions? i would also like to know how to do a leakdown test or if you have to take it to a shop to have it done?

Thanks