not sure about the forepeak door...but the Sabre 28 is one of the best boats, IMHO, ever built. It has it's quirks, curved floors, small storage. But it is well built and sails even better.
Usually if the mast step has been repaired you will see a slight difference in the sole. Mine had been repaired, but they redid the whole sole with similar material that Sabre did originally. Mid atlantic repairs usually use a thinner veneer product.
I would look closely at the door it should "hang" symmetrically and may just need an adjustment. Could be a land carpenter "fixed" it previously and may only need a boat carpenter to redo it.
Other than mast step and older electronics, you should be happy with the Sabre 28, especially an 80's model.