I have oil leaking from gasket or O-ring on oil cooler. Mazda says you have to buy new oil cooler = $400+. Is there a gasket or O-ring replacement available. 2007 Mazda 5 Touring.

An "O" ring can be purchased at your local auto parts along with your oil filter. Your oil filter screws on top of your oil cooler. Mine leaked as well. A new "O" ring and filter screwed on tightly solved my problem.

That is the oil cooler. Remove the oil filter. That exposes a large 'nut'. Remove the nut (and the 2 lines going in/out) and replace the oil gasket/O ring. If original oil cooler is dent or damaged, replace cooler as well. Could also just come from the lines going in and out of the cooler (put new hose clamps on).

Contact your Mazda dealership's Parts-Dept. w/ this Part-Number: LF8X-14-702 for the gasket, or place an online-order for twice the cost as my local-dealership:
http://www.amazon.com/MAZDA-CX-7-MIATA-COOLER-GASKET/dp/B00DQYG9D4/ref=pd_sim_sbs_auto_1/190-6912148-0373061

I just helped a friends save > $500 w/ this Mazda info. Ebay has options as well if you want to pay 1/4-1/3 of dealer-prices for the oil-cooler itself, which - as all probably know now - includes the $5 o-ring gasket.

Best wishes,
Nick
"Don't forget to (a) change your oil & (b) flush coolant."

that's because it's easy. it's like a radiator, disconnect hoses, replace unit, re-connect hoses

Yes,but there is a o ring type seal in it that needs to be replaced also.

power steering fluid??????

when does it smoke at start up or when running. if at start only likely valve seals are bad and need to be replaced, if smoking all the time bad rings or head gasket, if black rings are bad if white check oil and if water in it (oil is milky) bad head gasket all of these are exspensive repairs from vlalve seals $400-500 to headgaskey $800 plus rings rebuild $2000 plus

I own a '99 Isuzu Oasis, which of course is really and '98 Odyssey with Isuzu nameplate. 214,000 miles, Cranked it up yesterday morning after 20 to 30 degree temps that night....took middle schooler to class approx 3-4 miles from home and approx 1/4 mile from home- noted severe burning oil smell in cabin and smoke from under hood.. Got it home and observed 3-4 quarts of leaked oil on the ground where I had been sitting just 15 mins before. Thought for sure I had ruined the engine after seeing all the oil in the gravel. Could not believe the leak was so severe, considering this car still runs like a beauty and has shown no leaking or other symptoms in the days before this occurred. Got home later that day and checked filter thinking maybe it had loosened. It had not. Refilled engine with oil and noted oil not leaking or dripping but pouring through area at engine block and oil cooler juncture at filter area. Found this forum and a few others on line and followed the plan , AutoZone: loan-a-tool 30mm 1/2" drive socket is all you need to do the job, except of course the oil cooler seal/O-ring which I got at Honda for 3 bucks. Took me all of 45 mins...no need to dettach hoses and leak antifreeze, just unscrew the 30mm nut and remove the old gasket/seal. Be sure to remove all the pieces, Mine was hard and brittle and broken in 3 pieces. What once was rubbery/pliable would now snap like a pretzel due to age/wear. When I buy my next one of these, and I will, because it is the best vehicle I have ever owned ( and I have owned several Hondas and Toyotas) I will preventative replace this seal at approx 150,000 miles.... this was close to being catastrophic failure- Thanks to this forum and others for the advice-plan to put another 100,000 miles on this baby!

Oil cooler o-ring.
http://www.nissanpathfinders.net/forum/topic/25463-engine-oil-cooler-leaking-oil/
Not all coolers look like radiators. I wouldn't think it should cost that much. Try somewhere else.

common oil leak on those vehicles is the "quick connects" where the oil lines go into the oil cooler (what i believe you are calling the "doble") replace the o-rings on the quick connects for the lines