If the OP has been given the owner details by the DLT, he will know if the owner is farang or Thai and therefore what language to write the letter in.

I've just come across a classic Mini Cooper S with about 6 - 12 months dust on it.

My local bodyshop here has a few nice cars he has fixed a few years ago. The owners have disappeared and probably left Thailand, the cars are just gathering dust.

There is nothing he can do except wait for the owners to show. Until that happens the cars keep gathering dust, he cant sell them or do anything with them, and he does have the keys

Why would it be any different for you?

Yes if the owner does not reply then the car will continue to gather dust. Logical thinking says that something has to happen sooner or later. Towing to the wreckers or what? When parking places become scarce then I think somebody will make a decision on what to do. Anyway I don't believe there is nothing one can do about abandoned cars.

Any update on this?

I had to return to Australia for a few months on business.

So I couldn't check my mailbox at the condo yet,

but so far, no email, no phone call.

It's not looking too hopeful.