[san rensho]

The 3k vibration is a classic sign of a bad motor mount, another is a lot of movement in the shifter when accelerating after changing gear. If you change out the motor mount, replace the water pump at the same time if it has any significant miles on it. The water pump has a plastic impeller that will break up when it fails and send bits of plastic through out the head and block that can block the coolant passages and lead to overheating and cracked heads, etc.

If you do both the mount and the pump atthe same time, they are both very easy. To replace the mount, you have to lower the engine a few inches, which then gives you much easier access to the waterpump and to do the waterpump ypu have to remove several coolant hoses around the motor mount which makes replacing the mount much easier. IIRC, Pump is around $250, Mount around $150, very expensive Porsche coolant around $100.00.

Now to the IMSB (RMS is not terminal, just messy and can mess up the clutch) of which books worth of posts have been written online. Its a known defect but no one except Porsche knows the real failure rate. If it goes, generally the motor is completely detroyed and unrebuildable.

There are many cars that have gone 100k-220k+ mileswith no IMsB problems, other fail at very low miles, < 20-50k. Anecdotal evidence is that cars driven consistently at low RPMs, < 3000k, tend to have higher failure rates, while those driven on the track or "driven like they stole it" have lower failure rates.

Problem is that its hard to diagnose an IMSB that is going bad and catch it before failure. There is a classic rattle it makes before failure but the rattle can last for days or weeks, or just seconds before failure. Some never get the rattle. One way of diagnising a bad IMSB is to check the cam timing variation on the computer (Porsche or Durametric). If theere is a significant difference in timing between the cams, righ and left side, good indicator of a bad IMSB. Finally, metal and plastic (from the IMS bearing seal) in the oil filter is another warning of a bad IMSB. If you can, pull the sump plate and see whats collected in there.

There is an aftermarket replacement bearing that costs about $750 for the bearing and special tools needed and once the tranny is out, the replacement is a couple of hours. I don't have any signs of a failing IMSB and I'm going to replace mine when the clutch goes, but after the initial panic from all the IMSB horror stories on the interwebs, I've calmed down.

Pelican Parts, in the Tech section has good write ups on engine failure modes and IMSBs.

$9k sounds pretty good, I recently got my 2000 2.7 w 114k miles for $7500. Its definitely a buyers market out there. I would try to beat up the seller a little more.