Plenty. In addition to pure math which shows it is chaotic over periods of as little as a hundred million years, we see and continue to collect evidence from surface features that the climate has radically changed at different latitudes in the past.
Yes Star, that's the idea.
As the polar axis wanders (not sudden) Mars goes through large climate shifts, wet warm Mars, dry cold Mars.
This may have happened early on, but cannot happen now, because Mars has lost a lot of it's original atmosphere to space. So even if all the CO2 and water at one or even both poles melted the resulting atmosphere would not be thick enough to warm Mars up enough for liquid water. But we are not done looking for CO2 and water reservoirs on Mars.
The atmosphere is lost through; slow escape (low gravity accentuates this), stripping by solar wind (no large scale magnetic field for protection), bombardment (low gravity, thin atmosphere, near asteroid belt).
Mission wise you need to get to the layered terrain, take samples of each layer, and date them. Then this needs to be matched up with ages of "river/flood" deposits from all over Mars.