Hi there!
Most people do not think about this - but...guess what? You can wash it! LOL. I know it sounds...SCARY...but it works! We have been dealing with dresses for 28 years. I would say that it depends on the designer though - for example our dresses
are all hand beaded so we don't use any glue or anything like that. So, the deal is...turn the gown inside out, use a detergent like Dreft, cold water and gentle cycle. Hang to dry! You can also pretreat areas (like the hem). Will you lose a couple
beads/pearls? Probably...but you can also have them replaced pretty easily, if you wanted to. Because you have waited so long to clean it this may not be the perfect solution (set in stains could be a problem at this point!). A company that I have
worked with in the past was Wedding Gown Preservation company. You can buy their DIY kit from most bridal salons (or online). They do a good job, the gown will come back in a nice sturdy box, etc. Hope this helps! :)
Kerrie
http://www.mygownpreservation.com/