A few weeks ago I suspected a leaky head gasket on my 2003 Tacoma. I had replaced the coolant the week prior (first time since buying used truck, 200,000 miles, coolant looked like mostly water), and it sounded funny at startup (misfires, roughness) and seemed to lack power. A compression check confirmed a problem, with less than 50 lbs. on #3.
I pulled the head and, sure enough, the gasket was shot between the water jacket and #3 cylinder, and was ready to blow on #2. It looked like it had rusted out. The new coolant must have rinsed out the salts and expedited the leak.
I took the head to a local shop ( Monterey, CA) for cleaning and inspection. Although the head was not warped, there were cracks running from the spark plug holes to the exhaust seats. The casting would have to be replaced.
I could not find a replacement casting in the Bay area for less than $400, and it would still require valve job and machining that was estimated at $700 to $1000.
I searched on the internet and found a few for sale on Ebay. The best one looked like 'Odessa Heads" out of Clearwater, FL. They advertised a new aftermarket casting, fully machined, with new valves, assembled and adjusted with camshafts, ready to install, for $450, free shipping. No core charge up front, just return the old head within 30 days in the same box, prepaid shipping. It sounded too good to be true, but it was worth a shot.
They sent the wrong head at first (8 port, distributor) and apologized, sent the correct head 2-day express. Brand-new casting with used cam and lifters, but all the gaps checked OK. I had to deburr the whole thing, as almost every edge was razor sharp. But all accessories fit perfectly, all threads were well cut and straight, and it fit/assembled easily with no leaks.
I have over 1000 miles on it so far with no problems. Power is much improved and valve train is quiet ( used to have a lot of ticking).
If you have a need for a new head, I recommend "Odessa Heads".