well, after installing the UDF and seeing strange behaviour I reverted back to original firmware. So in principle it is the same as always but actually isn't, something went strange on the flashing stage (had to shutdown, disable, enable, several times...)
I don't know of any good drive debug tool, flasher, etc to start checking everything is fine.
I'm waiting to buy a BD drive to be released in Europe, but yes, I want to fix this, there's also a funny thing, the external DVD writer can't write SL DVD's only DL. So whenever I need to burn a DL I need the external, and when SL the internal, it's really weird, the external drive is also always spinning when I put a disc inside...
I'm clueless on everything related to optical drives issues so any help is welcome.