I wrote diamond@hilton dot com requesting my LTD qualification info and got the following canned response:
We sincerely apologize for any inconvenience as we have limited information regarding Lifetime Diamond. We appreciate your long term membership to Hilton as a Diamond member. I have created case in regards to your inquiry to Lifetime Diamond Status. Should you need to follow up on this request, please reference # XXXXXXX. Again, we sincerely apologize for any inconvenience this has caused and appreciate your patience and understanding.