as saute86 said even after you get it free it wont be that great and will squeak or screech as you turn while you fish so its best to just toss it all and this time use a pinless mount.
what im talking about is this:
http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313.TR0.TRC0.H0.X1. 77+seat+base&_nkw=1.77+seat+base&_sacat=0&_from=R4 0
whats nice about them is you wont have stuck, rusty, corroded, or bent pins to deal with or those plastic bushings to replace.
your 1.5" seat posts will fit inside the 1.77" posts like a sleeve without any play so what I did was get one post and I cut it in half then I cut the pins off of my 1.5" posts bolted my 1.5" post onto them to use as an adapter so I didn't need to redo the seat mounts.
not saying the best solution is to do what I did but I find it works great and I like it. its all aluminum so nothing to get rusty or corroded if you leave them in, and im a big guy so I bent a pin on many a post because the 3/4" pin design isn't made to handle much side force at all and can be bent way too easy IMHO just by stumbling against it.