Dr Ruth says,
Once they have got too dirty to be seen out in, think about buying new ones.
In the meantime, if you are amongst people who might notice how dirty they are, stand next to someone whose wearing much dirtier leathers than you. Yours won't then look too bad.
If you are really bored with absolutely nothing else to do, and your computer has gone down so you can't f*rt about on DSC message board or look at porn on the internet, try traditional dubbin to feed them, but don't overdo it cos you'll be sliding about on your seat.