Few materials are required to clean a set of hoods.  The kitchen sink, warm water, dish soap and a scrub pad.  There is also a secret ingredient that will do an incredible job of removing most, if not all, of the crud that commonly contaminates brake hoods.  The secret ingredient?  Good old WD-40. 

The hoods can be removed from the brake levers, if you wish, but it is hardly necessary.  In fact, when it comes to twenty something year old hoods, the less asked of them the better.  It might be best to leave them in place rather than put them through the unusually rough treatment experienced during installation and removal.  And, if you want to take the "in fact" argument a bit further, the levers need not even be removed from the bicycle, but it is best to do so.  I find it very difficult to fit the whole bike into the kitchen sink.

Start with a pair of hoods that are not dried out, severely cracked, melted or obviously beyond repair.  This is, at times, a "maybe or maybe not" judgment call, but that matters little.  You have practically nothing to loose by trying to clean the old hoods up.   If you do the work, and they don't clean up well enough to warrant use, you will have wasted a whole ten minutes and almost nothing in the cost of resources.  Small rips are not going to be a major issue and might even be repairable, using the Silicone Seal method mentioned.  I might add, that the Silicone Seal will have a much better chance of adhering, after a thorough cleaning of the hood is completed.

You can use an entire scrub pad, if you wish, but about all that is required is a quarter of the sheet.  Immerse the lever in warm, not hot, soapy water and try to brush any heavy debris, if present.  Squirt a bit of dish soap onto a hood and massage it in with your scrub pad.  Don't be afraid to use a little pressure.  Rinse the hood, and repeat, until you see no further improvement.  Perhaps this initial cleaning will be good enough, and there will be no need to use a stronger chemical for cleaning.  If the result of the soap only cleaning is acceptable, rinse the hoods off very thoroughly, dry and install everything back where it belongs.  You will notice that the hoods feel a bit sticky.  Don't let this bother you.  A couple of rides will get rid of the sticky feel, and things will be much as they should be.

If, however, the hoods still appear to be stained, it is time for the penetrating fluid.  You do not need a lot of this stuff to get good results.  I urge you to use it sparingly.  Though it is not a safe practice, from a dermatologist's point of view, I squirt a bit of WD-40 on a hood and then massage/rub/scour the hood with my finger tips.  Stubborn stains, needless to say, will get more attention than areas that are already fairly clean.  That said, ensure that the entire surface is cleaned with WD.  This will add to the uniform appearance of the finished product, by helping to avoid blotches.

It would be wise to wear rubber gloves, when using any solvent or chemical.  Most solvent based products, and WD-40 is solvent based, will damage delicate skin oils and lubricants.  I have spent years in industry, as a professional Millwright, and know full well the damage that chemicals can, and will, do to my hands.  Best advice is to use the gloves but the choice is certainly up to the individual.  I, in my carefully crafted stupidity, choose not to most of the time.

After thoroughly massaging/rubbing/scouring the WD-40 into the hood, do your best to wipe the hood and brake lever clean of the penetrating fluid.  Wash the whole works off in the sink with the warm soap and water procedure already mentioned.  Now, take a look at the results.  Are there any obvious stains remaining that you might be able to get rid of with a bit more effort?  Does the surface look uniform?  Questions such as these, and the answers to them, will determine if you want to go through it all again, with hopes of even more improvement.

Once satisfied that the hoods are as clean as you can get them, they need to be decontaminated a final time.  Drain the sink and rinse it out carefully.  Now ,with the warm water still running, apply soap directly to the hood and really massage it into the material.  You should have the water a bit hotter for this process.  After rinsing, dry the assembly and smell the results.  You don't want to smell the WD-40.  You want all traces of odour, gone.  It is a petroleum product and prolonged contact with the hood material will cause, or accelerate, deterioration.  Also, you don't want this stuff on your hands while riding.  Do a good job of decontaminating the assemblies.

And then install the nice looking old levers back on the bicycle.  If all goes well, you might well have save yourself the price of an evening out.