Been through one several times this winter. I don't like the soap, but it beats the hell outta me doing it in 35F and rainy weather. Never noticed a leak. As to the soap eating the seal??? if that happens, BMw better step up. That would be absurd.
Pretty soon I'll have my external hot water hose bib plumbed and I'll hand wash from them on out.
'15 3500 HD Dually