I know this is a very old thread, but I had the same problem and could not find an answer.
I've just tightened the front weight on my Ultima S-line.
Obviously, I turned off the power first.
The washing machine casing is welded together preventing front access.
What I did was to turn the machine upside down so that it rested on the top weight.
I then undid the shock absorbers.
This allowed me to push the drum as far back as possible.
I could then get a ratchet socket spanner in to tighten the screws.
I was unable to see the shape and size of the screw top.
The best fit seemed to be a T40 Torx/Star bit.
I then refitted the shock absorbers and righted the machine.
Be careful to ensure that the top springs remain attached.
Ben, May 2020
