A modern automatic transmission is a very complex piece of equipment with a whole bunch of parts that have to be talking to each other for it to work properly. Your best plan of attack is to have the vehicle inspected by a transmission specialist who is familiar with this transmission and should be able to diagnose the fault.

But it sounds like there’s something broken or loose inside that is not allowing the engine’s power to be transferred to the car’s wheels. This could be anything form an input or output shaft, a clutch assembly, torque converter or even the gearsets themselves. Perhaps the fault is in the valve body (the part that actually selects each gear) but until it’s torn down and inspected, you won’t know what’s going on.

The other major cause of a car not moving when it’s in gear is that there’s a broken driveshaft or CV joint. The symptoms can be very similar, so check the whole driveline before committing to repairs.

The Santa Fe may well have a fuel filter below the rear seat, but it’s almost certainly located on the outside of the car (as in, under the floor) rather than inside under the seat cushion. I’d be very surprised if any of the car’s fuel system or lines ran inside the passenger compartment.

Which means it’s still possible that some fuel was spilled under the car during the filter change or that there’s even a fuel leak as a result of the change. Either could lead to a smell inside the car, but it shouldn’t persist. If it does, there’s a problem. Take it back to the dealership and ask for the problem to be fixed. If the dealership somehow spilled petrol on the seat trim or allowed fuel to enter the cabin in some other way, they are responsible for fixing it. Driving around in a car with petrol fumes inside is an obvious health and safety issue.

The default purchase for somebody looking for a mid-sized hybrid SUV is the Toyota RAV4 Hybrid. But if that’s too big, there’s the Toyota Yaris Cross Hybrid, C-HR Hybrid and even the Corolla Cross Hybrid which sounds like the marketplace is getting crowded but is really just a reflection of the appetite right now for cars like these. And that’s the catch; the waiting times for a brand-new example of some of these cars is out to many months and even years. So your plan to shop second-hand makes plenty of sense, but don’t expect any bargains in a market currently being dominated by lots of demand and less supply.

Beyond the Toyota brand (which has been doing hybrids longer than just about anybody else) there’s also the Mazda CX-30, Subaru XV Hybrid, Haval Jolion Hybrid, Kia Niro, Subaru Forester Hybrid, Nissan Qashqai e-Power, MG HS, Honda HR-V e and more. For something a bit bigger, try the Kia Sorento or Hyundai Santa Fe hybrids. There are others out there, too, that are probably bigger or more expensive than you need, but it's very much a growing scene in the Australian marketplace.