Please tell me what make of Waterman this is.

This is a relatively heavy pen with a brass barrel. The nib is an Ideal 18 K 750 with ST initials on the back of the nib. I obtained the pen in an internet deal. The ink does not flow steadily and skips when writing. I wish to purchase additional nibs and do not know if this is possible or how to specify which nibs I need. Thank you in advance for your assistance. WJH