WeAAsles,
Unfortunately, Part-Timers have been taking it in the shorts since the TWU days of America West: unpaid sick days, higher insurance premiums, family coverage denied (employees only), etc.. IAM had its own differences in particular on furloughs without guarantees of a job in the system, no moving expenses, and certainly no "juniority", and of course, higher insurance premiums and lower pension benefits.
I think the attitude was that Part-Timers weren't "serious" as this was a second job for "play money" and travel benefits, while Full-Timers were raising families and more committed to their jobs, thus favoritism was granted towards Full-Timers.
Personally, I have come to realize that being part-time or full-time are often times just labels as there a many Full-Timers who work part-time hours and Part-Timers who work full-time hours. If the degree of "seriousness" to the job is measured by number of hours worked, then it seems fitting differences in benefits should be based upon hours worked, not on whatever label has been assigned.