trying to keep the radius traffic from a router to use a fixed WAN interface without success.

The network:
OSPF enabled so the route to 0.0.0.0/0 is dynamically added by OSPF, there are two of them (10.10.0.241 and 249 being the gateways), so as a result I have
ADo 0.0.0.0/0 10.10.0.241 110
10.10.0.249

This router is also a PPPoE server, that authenticate clients against a radius server (on the cloud).

The problem, is radius server (DMA radius) sometimes count Online Time and Traffic over the same period, if it gets packets from a different IP address, even though the Caller ID remains the same.

things I have tried so far
* use policy based routing by Mangle connection and create Routing Mark, does not work and I think OSPF rule ticks in before my static routing
* use Mangle rule with action route. While this does force routing , it can only be applied to Prerouting Chain. The radios authentication packet is from the router itself so it's Output or Post Routing Chain, Neither of this two chains allows action: Route.
* added static route in the routing table It seems to be working but the new issue is that once client is offline, it is not able to authenticate again. The error message is Authenticate Failed

I have allowed simultaneous authentication on radius (in case the previous connection is not killed by radius when the router is making new request), I have tried to block request from PPPoE client in Bridge Filter for few minutes and allow it again. None worked. The only think that worked was to disable my static route and allow the router to pick, then they all authenticated in few minutes.

any help is appreciated.