Thanks, lots of great information, should be of value to many readers of this thread. Just for discussion, I decided to drain the rear differential with the car on the garage floor, I didn't even raise it on low ramps, so I had more difficulty developing much torque with my outreached arm I just looked up the torque, surprised to find it is 30 ft-lbs. I carefully watch all fluid changes, oil included, by putting a clean piece of cardboard under the drain plug area and coming back in a couple of hours and look for any drips - of course I wipe the plug area well before putting starting the drip test. This was my first rear differential change and the only other person to have their "hands" on my Forester is the dealer, and never for service. But when they get the car in they do a general check over and come up with $500 + recommendations for fluid/grease change. I always figured that was a good deal, they are looking for more profitable work and should be good at finding real problems too. Now here's one for you, given what I just said, I yesterday pulled the glove box to gain access to the cabin air filter. I figured it would be time to change as it is recommended at 30K and the car has 55K miles. Wow, open the filter housing, no filter! Now where did it go? Anyone's guess, but the only two I can come up with is 1) factory error, 2) dealer took it out and forgot (?) to put it back during one of their look for work efforts. The car has been to the dealer twice, once for tires and once for a recall. The '04 Forester has a "crush" washer on the oil drain plug, and when not changed/replaced at least for a few (I wasn't counting) drains it may start to drip very slightly. I was in Advance Auto yesterday to buy ATF to drain/fill the auto transmission (just the pan, no power flush)and asked after purchasing some new crush washers. They had some, per their computer, but had trouble finding them. They must not be a big seller. I have never replaced an oil drain plug washer in any other car and I've kept one of those to 200,000 miles. There may be an oil drain plug replacement with a better washer arrangement. I suppose the auto transmission drain plug is the same. But as this is the first time it is off, I'll just reuse it.

afg,, "I dont think one can compare if you did it your self with a "home" filter and if one went to a garage, and they put in a "home" filter. One has different expectation in that case!" There should not be a different expectation, but the perception that it is OK for someone who is decidedly inexperienced, and uneducated in the field of automotive maintenance to hack something into the car and it's being seen as both cheaper and of reasonable quality underscores one of the reasons mechanics can do their jobs correctly and still be treated as if they are dishonest while doing so. While doing training for a large retail chain recently, one of the area managers asked me for some possible ideas about why they have difficulty retaining technicians. The poor ones stay, while any that have real potential to be good move on in less than two years. The way they market attracts a great number of customers who would be likely to see such hacks as attempting to cut a house filter instead of installing what belongs there as genuinely a good idea. There is a cost associated to such attempts at savings like that air filter hack. This company is so directly affected by it that when I asked him back if he would want his son or daughter to seek a career as a technician inside his company he admitted that would not be desireable.

We see this problem all the time and more than likely your Return Duct leaking or sucking in the dust, since the supply air is blowing air OUT, your vents, and the return duct sucks in and I'd bet it's the area directly behind the filter grille. Is the wall cavity above and below the grille covered? also are the panning edges and headers sealed with caulk or tape? If they're taped, then that could be your problem, tape doesn't last like caulking.

Your Honda may have a "cabin air filter". If so, smoke smell can linger in it. Check the maintenance section of you owner's manual. The filter is replaceable. I have a Honda CR-V and its cabin filter is located behind the glove box. If there is no air filter, a cabin scent hanger may help mask the smell. A popular odor is "Pine". Used car dealers often hang these things under a seat to aid sales. Scent hangers are available at auto supply stores.