Ive valeted a fair few mouldy interiors in my time. 'Usually' they turn out ok with just the usual clean. The most important part is to make sure the seat and carpet is bone dry before putting it back in. It really depends how far its gone and how deep the moulds got but you should be ok. You can get some good mould killers that should do the trick if you must. Obviously a full interior strip down will be needed to do a thorough job.