Do I have to drain transmission fluid to replace cooler lines? Also if rubber is cracked open does that mean for sure there is a leak?

Hello, first, the cooler lines may have rubber split but may not be leaking - yet. It still sounds like an area that would need attention. Replacing cooler lines does not require replacing fluid, but you may need to top off anything that comes out that may be in the lines currently. The fluid leak may or may not be coming from those lines; sounds like you may need to drill down to the source of the coolant leak first and foremost before doing any repairs. Have you looked at the axle seal areas? That would be a fairly common place to have a leak originate from. You can perform a leak test by having dye added to the transmission fluid to then use a black light to find the root cause if it's difficult to find. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops