Did you consider that the rim may not have failed because of an impact? I had an incident with my Lexus GS300 when the tyre went flat, as described. I took the wheel to a local Renault dealer here in France, and he called back - 'You'd better come and look at this...' With the tyre off the rim, it was certainly cracked, but no sign of any impact damage, and I was sure I hadn't hit anything. After a great saga that finished up with me writing individually to every director of Toyota in Tokyo (because Lexus France were utterly unhelpful) they finally admitted the crack wasn't caused by an impact and replaced the wheel free of charge. Some weeks later I mentioned it in passing to another guy who said, 'Oh yes - my Dad had exactly the same problem'. I was damned glad it didn't happen on an Autoroute at 150 kph.

 

Get the wheels professionally welded. It should only cost about $80-100.

 

I literally just dealt with this exact problem a month ago lol. Except in my case, my Front Passenger wheel had a Crack in it and I was experiencing all the symptoms you described as well. It turns out that when I hit a huge pothole on my way to work I had screwed up the inside of the wheel and it was causing air to escape

Anyway , I just Google replacement wheels for my car (06 RWD IS350 with factory 18's) and came up to a site called PartsGeek.Com they had the wheel for $167 after taxes. I bought it and waited a week and a half for it to arrive and Voila!! Good as new!

Seriously though. Don't ever buy ANYTHING from a dealership unless you absolutely have too. My brother bought a replacement wheel for his IS350 off eBay for an even cheaper price than I did but I don't trust Ebay soooooo....

Anyway good luck with your search and hopefully I helped

 

This thread is more than four years old; I'm sure the original poster has already taken care of his leaky rim.