One problem related to transmission fluid leaking has been reported for the 2003 Toyota Tundra. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 Toyota Tundra based on all problems reported for the 2003 Tundra.
When returning to my2003 Toyota Tundra, from a doctors appt, I noticed a pool of liquid, under the rear axle of the truck. Having wife back truck up, I checked this viscous, clearish fluid, finding it to be a rear end oil/grease, and had been leaking from mid housing of the rearend. Upon further inspection, I found this had been leaking for enough time that oil spots were all over the rear window of and tailgate of truck. I called Toyota to look at it and they wanted ?$120 just to look at it, so I brought to a mechanic down the road form Toyota and he found the rear axle housing had rusted thru. He in 40 years had never heard of this problem, and while searching for a replacement rear end, could only find one "good used" one in new england. He obtained and replaced my damaged one, for a cost of >$1000. He later told me he had another one come in less then a week, same problem. At home, I found oil had been leaking front the back of the truck for some time, evidenced by oil on the ground and wood near where the back of the truck was backed into driveway.