Is your wheelchair not able to be driven to your dealer for repairs? When this is the case you should always use a flat bed type of transportation. If you have access to a trailer you can do it your self, if not you should inform the company you call that the vehicle needs a flat bed as it's the recommend type from all wheelchair conversion manufactures. When done properly you can be insured that the vehicle will not have any additional damage to the vehicle during the trip.
Almost all minivans are front wheel drive and would require you to lift the front wheels to tow it down the road. During the conversion process the fuel system is moved to the rear and other features such as flares, trim pieces and hitches will be positioned closer to the ground when raising the front of the vehicle in the air. During the trip the driver will encounter dips in the road, rail road crossings, speed bumps, steep driveway entrances all which could cause additional damage to your vehicle that will cost you more than the tow bill itself.
Full size wheelchair vans are more commonly rear wheel drive and can have the front wheels raised with less concern about ground clearance at the rear. However, if you have a All Wheel Drive full size wheelchair van it will also require the flat bed type to transport your broken wheelchair van to the dealer. In general the cost to have it flat bed will not be much more expensive but it will offer you the piece of mind of not damaging the vehicle during the towing process and will most confidently not cause any damage to your transmission or another drive systems component.
Start with calling your mobility dealer that you purchased the vehicle from to see if they have a preferred company local to you they would recommend. Often your dealer will have a relationship already established that comes with experience of towing wheelchair accessible vehicles. If the driver that is sent to pick up your vehicle has no prior experience towing these types of vehicles they are more likely to cause damage during the loading and unloading process. Lack of experience could result in the driver dragging the vehicle onto the flatbed with all the wheels locked in order to complete the job. Often this happens when additional modifications completed to the gear shift or steering systems that differ from the original design.