My experience buying a rebuilt engine for my 2001 MR2 from MonkeyWrenchRacing.com
Long story short: I had to try to fix their rebuilt engine and ended up ruining it myself.
Long story long: At about 135,000 miles, my 2001 MR2's 1ZZ-FED was burning at least a quart of oil every thousand miles.
I spent about $5,000 on a rebuilt engine from monkeywrenchracing.com and a bunch of other stuff that seemed sensible to replace at the same time.
I got it installed and ran break-in oil and then replaced the oil. I took the first couple hundred miles easy. The engine was burning a lot of oil, but I was hoping it would go away after the rings wore in. A coworker suggested driving it with a bit more punishment to help things wear in. A couple hundred miles more and it was still burning more oil than my original engine. A bit of research and an email from monkey wrench racing pointed in the general direction of a bad valve stem seal. I contacted monkey wrench racing and they offered to have me send it back to fix it or they would send me new seals and a refund for the shop time to do the job. This is my daily driver and I couldn't keep borrowing my parents' vehicles, so I opted to try to replace the seals myself. It also seemed like less work than swapping engines again. After buying a specialized tool ($100ish) and a lot of fucking around, it was finally ready to test drive. It ran fine for about a mile before I heard a "clunk" and lost power. I got the car home and remembered: I forgot to tighten the exhaust cam sprocket bolt. It was barely finger tight. It came loose and the valves smashed into the cylinders. I took the head to a respected local engine machine shop and got their advice. When I dropped off the head I was told there was possibly a head gasket leak indicated by a cylinder basically being steam-cleaned by coolant while the other 3 were fairly dark. To get my commuter running again, I ended up finding a 2007 (post-oil burning issues) corolla 1ZZ-FE from a local salvage yard for $700. So far it has been running fine. Later I got a quote from the machine shop and decided not to have the head refurbished due to the cost and not knowing whether the pistons, connecting rods, etc. were any good. The disassembled engine now sits in my dad's shop storage until I figure out what to do with it. I'm definitely bummed, but it's not like I can completely blame MWR for me wrecking my engine. I thought it might be a good idea to share my experience so others researching options for their oil-burning MR2s have an idea of what they might be getting into.