RouterOS does not redistribute default gateway, you would need to set each peer to distribute default of it's installed but this is unfortunately not always stable...
RouterOS design is to use OSPF as IGP so you could advertise default if installed by eBGP and adjust the metric using route filters, if you want the one router to offer default gateway via OSPF and the other via eBGP.
I have two Mikrotik Routers installed and both have EBGP peering with an ISP. ibgp is also configured on both routers. I want to prefer default route received via one ebgp peer over other through local preference but my routers are not communicating local preference over ibgp. is there anything I am missing ?