How should expenses be split?

I took over a portion of the land my dad rented a couple years ago and a share of the equipment. Dad is 480ac and I'm 530ac. I have bought more equipment since then to upgrade older equipment of his and just add to the farm. I have 2 tractors and he has combine and a tractor. Currently we split fuel 50/50 and shop and grain bin site. Now he wants to split the equipment maintenance 50/50 as well instead of he pays for his and I pay for mine. He's had financial issues over the past couple years which is why I've taken over more and more. The problem I have is basically every time he comes up short on money I get a call asking for me to take on more. I'm just trying to figure out what is fair and best ways to go forward with him want to transition to me having more ownership. Btw it's 2 separate operations farming together.