When you get your new seat and post, take a section of old chain from the co-op, run it from the seat rails through the chainstay/seat tube junction and have someone help you pin it together. Thieves typically do not carry a chain tool with them and chains are pretty hard to cut through. Works even better if you also get an old inner tube from the co-op and put the chain through it before pinning; keeps it from rattling around too much and damaging the paint.
Post what you need in seatpost size here before you buy, lots of us have boxes of them as well as used saddles. If I have one in the right size for you you can have it and a saddle for the cost of postage. I'll toss in a length of used chain, a pin and a tube too.
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Last edited by rccardr; 12-21-16 at 02:28 PM.