I have just reread your post, and if you have spent $4000 already on the engine, you will feel a strong temptation to stay with it. I urge caution thinking that way. This is my engine saga, I am not proud to reflect on it, but it taught me a lot:
I bought my boat with an Atomic 4 nearly ten years ago. I was clueless back then, the surveyor said the engine was in good shape, I now realise he was more familiar with much more expensive boats. I started having problems fairly soon, and my first thought was to replace it with a new diesel, rather than deal with the inevitably long process of all the bugs that would come out. Most of the advice I got (this web site did not exist then) was that the thousands the new engine would cost, even doing much of the work myself, would be a waste on a boat with good light air capabilities; and the old engine would probably be fine with some work. Against my own instinct, I kept the old one.
Despite my efforts, my lack of engine knowledge, combined with years of past neglect, made that a bad decision. Over the next couple of years, I got very good at sailing in and out of the slip with no engine - I can credit the engine with getting me some recognition from the old salts at the marina.
After over a year, I thought again about just buying a new engine, but the lack of any available replacement that would fit without carpentry made me plow about $2000 into the A4. It still gave problems, I still worked endlessly, gaining expertise slowly, and finally seemed to have put it right nearly five years after starting. The work had included replacing the water pump, adding a raw water strainer, replacing the thermostat, acid flushing the engine, replacing all the hosing, replacing the fuel filter and adding a second filter, replacing the fuel pump, cleaning the carburetor, replacing the ignition panel, instuments, and all the wiring (after a short circuit started a nasty electrical fire at the engine, thankfully I shut it off before fuel got involved), replacing the control cables, replacing the transmission gasket, replacing the stuffing box and cutless bearing, cleaning the distributor and replacing the cap and spark plugs, retiming the ignition, adjusting the oil pressure and replacing the sending unit, new mounts, and probably more that I can not immediately think of.
Fate did not want it to work, and on my first day of sailing with an engine sounding sweet, and all the gauges reading right, it suddenly cut out without warning. It would not restart, and I had to return to port with a canoe paddle, along with a girl on our first date. I tried to troubleshoot, but all I could find was that the compression, which had hitherto been good, had dropped somewhat on all four cylinders. I gave up, and called in a mechanic who assured me that it must be a simple fix if it was running smoothly before it died; but he achieved nothing other than costing me money. I finally hauled it, and sent it to Don Moyer, who found that the block was cracked, and replaced the engine with a rebuilt one for $5000 (I was locked into an agreement by then).
So... after around $8000, and several hundred of my man hours, I had a working old engine with all new parts; but I never got to use it, as it got flooded in Hurricane Ivan, and I had to haul it again. The insurance covering the boat was no higher with the rebuilt engine, as it would have been for a new one, so the story has an even more expensive end: I am now buying a new diesel; had I done so ten years ago, I would be several thousand dollars better off, and would have had a lot more days of sailing rather than head down in the bilge over the last ten years.
Every case is different, as your case may be to mine (without seeing the engine, your Ericson breathren can only offer general advice), but what you have described sounds horribly familiar. Consider all your options carefully, as sometimes the cheap fix works, sometimes it turns out to be an illusion. Over ten years I have learned that a lot of jobs that seem over your head when you first consider them, are doable with patience, plus they make you a far more capable mariner at the end.
I would sum it all up by saying that a well looked after engine can run on and on for years, but an engine neglected by a proponent of throwaway culture is best thrown away.
I doubt you have any legal case to stand on. I have taken a boat yard to small claims court, and won full claim plus costs, but my case was pretty black and white. In your case, 'as is' usually means they can have lied through their teeth and get away with it.
If your mechanic has charged you $4000 to deliver you a piece of #$%@ of an engine, and wants another $4000 now, you need to get the local chapter of the Ericson owners association to don horned helmets, face paint, and loin cloths, pick up some heavy tools or farm implements, and pay him a personal visit.
Gareth
Freyja E35 #241 1972