Greetings,
I'm a software architect with a master degree in complex software engineering.
UML diagrams are in the center of my abilities.
I'll be glad to work on your sequence diagram, i'll deliver the work with all comments and OCL contraints needed to avoid any ambiguous understanding. so feel free to contact me and have a nice day.
NB: i work on ArgoUML or StarUML but i have no problem using other modeling software.