Only apply primer to concrete roof?
You really need a sealer. White is chosen to reflect the heat AND this will last longer than black. When we used hot tar on roofs we then painted them silver or white. If we did not do this the tar would end up in puddles. 

Primers are made to seal wood and wall coverings, not a concrete roof. You need a coating with some “body” that maintains flexibility and don’t go cheap, get it sealed before it gets worse. Multiple coats may be needed but a quality product will probably work with one coat based on your description. 

So get the right product for the job and don’t go cheap.

Edited: I noticed the link for the Elasto lock , read the instructions this product suggests power washing, they mention acid etching to clean newer pours and do not mention primer at all. DO NOT USE PRIMER WITH THIS PRODUCT!. It needs the porosity of the concrete to bond as I have mentioned in several comments.
But I believe it would be a good product to use to seal your leak.
As I have not used the satin sealer in the original question I looked up some info. A question was asked about a concrete roof leaking here is rustolium’s response:

Rust-OleumSupport
March 04, 2019
Thanks for reaching out, Richard. Rust-Oleum Sealkrete Clear Seal Concrete Protective Sealer will offer waterproofing qualities, but you may need to consider two coats for adequate coverage. You will get 150-300 sq ft of coverage and you can recoat the product in 2 hours. - Rust-Oleum Product Support 1

So so as I said I would not use that sealer it only had sealing properties,  but the ElastO lock you linked to looks like a good flexible product made to seal cracks. And no priming is required but cleaning is.