What size crush washers will I need to replace if I change the oil filter and clean the gauze strainer?
Sure, 1mm x 22ID x 28 outside. I will point out that these are not genuine Ducati, but it's the size that fits and I've used them for years without issue. As you can buy them cheap on ebay. They are aluminium
Is that size for the sump plug? The oil strainer cover size is shown here as 30x23.2x2 https://www.corsasbk.com/product/78710091a/