This has been brought up before. I suggested JB-Weld against the warnings of many due to safety concerns. Well, the other poster tried it, it worked, and he was satisfied with the results. Of course the safest route is to replace with a new one, but when you have no viable alternative (melting the plastic using a plastic weld technique was suggested, but you'd better have a clean tank and luck on your side), JB-Weld is worth a try. Just check it every time before you mow to ensure there are no leaks.

I assume that the leak is not serious (size) if so as Larsol indicated a epoxy base sealant like JB will not be attacked by Fuel . I too hesitate with Rider Mowers with such recommendations since the leak could worsen and you or another innocent victim could be seriously burnt sitting a top of the fuel and ignition source . If the ignition source muffler etc is not obviously right below the leak you may feel comfortable with this method of repair. If the part can be replaced , replace it if not JB properly applied could be quite effective .

Thanks for combacks. Trouble with buying a new one is they are made so sorry,that it will probably leak in the future. The tank is so made that it is also the dashboard(copied the location of old Model A gas tank)and where it leaked was nothing hot or electrical. The air line is about 8 inches long and the one end extends to the top of tank and the other about 1/2 inch outside the tank,where a hose connects to it and it extends thru a hole in the frame. What a design,if you filled the tank to the very top,couldn't gas,under certain conditions escape out the bottom on the mower deck.(or would pressure keep it from doing that) Shouldn't it still work ok,if I plugged the air line hole and then drilled a small hole in the gas cap.(like some newer ones have) Does JB weld make a plastic weld? Thanks

I would not suggest drilling a hole in the filler cap. When a cap is utilized as the atmospheric vent, the cap innards are configured so the hole on the side where the gas is does not align with the hole on the outside. Since this fill cap is exposed (and looking at the IPL appears to face the operator, a hole drilled in the cap would spurt gas out the hole and maybe onto the operator when the gas sloshes around in the tank.

So far as I know, nobody makes any kind of solvent that will attack polyethylene, therefore, no type of glue repairs are viable.

JB Weld does not bond to polyethylene, but if it were to be "forced" into a crack, it might serve as a "stopper", but it will not get any bite into the plastic tank material.

Of course the Sears IPL does not give a visual of the fitting port, and no other pictures are available.
The fact that an O-ring is used tells me that the threads in the tank are not "pipe thread" (NPT).
Where exactly is the threaded port located on the tank?
The fitting that threads into this port, is it a 90 degree ell or is it a straight fitting?

JB Weld Black will Bond to either PP or PE Man Made Plastics . As I indicated JB Weld when applied Properly would be an Adequate Choice . The secret is within proper plastic preparation . For the chemical action to work within Bonding pre cleaning and etching must 1st be introduced. Any Ketone or Alkyl Acetate Solution will suffice. In more stringent usages Mild Concentrations of Sulphuric or Chromic Acid Solution are used then the surface is Neutralized with Mineral Water and dried. Much easier and just as efficient is the use of a Oxidizing Oxyacetylene Torch Flame . The Plastic section is heated carefully until glossy then let to air cool slowly . Rinse with Mineral Water Pat Dry . So you see why I recommended the replacement of the plastic part if at all possible . There are some Hot Glue systems that also work well on Plastic but would be suspect on your application due to ambient vibration and Fuel Chemical attack over the yrs . Again the Ball in in your Court , a little JB added to the internal threads may well seal ok . External Leakage will require the etching method of some sort for a permanent Bond .

Thanks again for all information. Called 3M and they also said that there is no glue that will stick to that kind of plastic permanently. Mownie,the 8 inch(or so) vent tube screws into the bottom of tank. It has regular threads and seals with an O ring. The leak was caused by a small crack in the threaded hole in the tank. Since it had to be plugged,I cut a piece of plastic from the dash part of the tank and used my old weller soldering gun and after about 4 tries,got it plugged. I checked a gas cap that had the vent and noticed it has a round baffle with a small hole to shield the hole in the cap. The cap on this one had the same baffle,but was used to hold a cap plastic retainer. I removed the retainer and drilled the hole in the top of cap and it was now shielded like the newer ones. Had fun removing the back tire,since have done this before didnt look for any trouble,but it wouldn't come off,so I cut the tire off rim with jig saw and and still couldn't get it loose from the rim till I took a chisel and cut the steel bead of the tire. Found a tire on internet for $18,Sears wanted $50.