Hi,
1) Gratuity calculation using termination work bench (pc00_m40_term) logic is attached in the below sap link.
http://help.sap.com/erp_fao_addon10/helpdata/en/94/129091bdcb4d1cbbbb6c86fb1211e1/content.htm
2) IT15 is used for making payment to the retired employee. You can also calculate as per your own logic and can be entered in IT15), if standard logic is not suiting your requirement.
3) You can also use the PCR as mentioned in your link (which is very nice). But mostly, try to push in configuration part so that, it easy and can be understood by others.
regards,
Bala.