I will be doing a T5 swap soon, and am running over my checklist. I've read that you need a new master cylinder, but have had no luck in finding out why? Someone said you can use the same one from the auto car, that you only have to mount the slave cylinder resevoir onto it. So does anyone know why you need a new master for the T5 swap?

your brake master cyl should be just fine. You will need a clutch master cyl to activate the clutch slave cyl. The clutch fluid reservoir attaches to a bracket that in turn is bolted to the drivers side of the brake master cyl.

Sorry I am stupid. I was completely forgetting about the clutch master. LMAO sorry.