Hi Anon -- Firstly, please realize that almost *everything* you read here is someone's opinion. The questions you are asking fall under the general realm of "legal" and since I am not a lawyer the opinions I am about to express are worth pretty much what you're paying for them.

That being said, you should start by reading your Proprietary Lease. Most PL's for co-ops formed in the 1980's and after used a standard template. There should be sections in your PL that delineate which areas in your building are "common" and the responsibility of the co-op corporation, and which are proprietary to individual shareholders. Read those sections carefully because the wording is sometimes confusing.

1) In my building, we interpret shareholder responsibility to be anything that is within the envelope of the unit (i.e. four outer walls, ceiling, and floor) to be the responsibility of the shareholder. Anything outside of the envelope is common area. The PL carves out a few specific exceptions, but for the most part this is how we decide. One of the reasons for this is the co-op has very little control over the quality of changes or updates made by a shareholer to their unit. If a radiator was replaced and the contractor used sub-standard parts and shoddy workmanship, the co-op cannot automatically assume financial responsibility for their repair or replacement.

2) The cost of the work will come out of your pocket. Unless stated otherwise in the PL or House Rules you are not required to use the building's super to make the repairs. You should be able to bring in a licensed and insured plumber from the outside. Check with the board for any rules they may have about this. You will need to coordinate with the super because at some point the steam or hot water will need to be turned off to your apartment line while the repairs are underway. If there are no definite rules about using the super, to keep from ruffeling feathers, you might ask him/her for a cost estimate and then get competative bids. That way your decision will appear to be a purely financial one.

Check with the insurance company that carries your co-op owner's policy to see if any part of this is covered and if it is worthwhile for you to file a claim.

Finally, ask the attorney who handled your purchasing of your unit. He/she should have read your proprietary lease and may be able to give you more than the opinions I've provided above.

Good luck!