Last year I dropped the trans
pan, cleaned and replaced the filter and gasket, and added new trany fluid. Everything went well. . . With 136,000 miles, I decided to do similar work to the engine oil pan. This necessitated removing part of the exhaust system, but I eventually connected to all the oil pan bolts, and the actual removal of the pan was without further issue.
I liked seeing that what little engine oil remained in the pan had not turned to sludge, and felt justified over having used synthetic oil - in place of regular engine oil. Further, there were a couple of spots (the size of nickel coins) where the paint had hardened and cracked (I imagine from heat) on the inside of the oil pan. Other than that, the pan cleaned up nicely, although I had to use a wire brush fitting on my drill to remove parts of the 15-year-old gasket that had hardened over time. This took more time than expected.
The oil pan was reinstalled - along with the original section of the exhaust system. Everything appeared to have gone well until it came time to replace the engine oil drain plug. Upon tightening the engine oil plug, I ended up stripping the screw threads in the oil pan drain hole. I don't remember seeing anything about this issue in the Highlander Forum, and apologize if I missed someone's entry.
Upon reflection, I think my use of one local mechanic or another, to change engine oil, may have resulted in the over-tightening of the engine oil pan bolt. I ordered another oil pan today, "O" ring and bolt, and will attempt to replace the oil pan next week. I am crossing my fingers that nothing else goes south. . .