Someone told me that Astro optical dont do SiO overcoat and that would explain the price difference. Its worth asking.
I would try the washing again. I use dish washing detergent and it probably cant hurt to make a fairly strong soapy solution and a bit of a soak, just as long as you give it a thorough rinse under the tap before the de mineralised water rinse.
If the coating is ruined its worth pricing a replacement mirror. Andrews sell them, or conversely get the figure touched up before recoating
