you have to sponge the seal, especially its grooves, with cleaner to remove the sludge.
have you emptied the filter, and did you remove the drawer and cleans its aperture?
if the washer has a bad load of resident soap sludge, the first wash will start loosening it, but you have to carry on until it's all gone.
Give it another hot hot hot wash with soda crystals and some old cotton towels (NO POWDER). If the water foams up and goes grey, that's the old soap sludge dissolving. Do it again until it stays clear.
If you don't add any towels or other load, it will (probably) try to do a small-load wash and the water level will be too low to wash the whole tub.
Old cotton towels are good because they will not be harmed by the hot wash, and are quite heavy.
Leave the door and drawer open after each use so it can dry out and discourage mould.