thanks Myleschetty and HCP! I believe my .wallet files are OK because multibit itself, multibit_recovery and other scripts seem to behave well managing the files. I understand hashcat does not manage the wallet, just the key. I believe my private key extracted is correct. I was wondering if there is a way to tell if a key has been corrupted (any parity, checksum, redundancy, ...). I'll keep trying in any case, thanks!
do you recovered your password. you also need consider the language and keyboad layout. both affect the correct password you set on the wallet. encoding also modify password sometimes.