I bought my 11s early November. It does a daily clean downstairs and a weekly clean upstairs in my little house. Just me, no pets so it’s not a hard life.
In six months I have had 3 brush guard rubbers tear and needed the guard replacing. At £7.99 for 2 months work that would make it an expensive game. It may be the layout of the house, short pile carpet, thickish rug and laminate floor, but since May I have tried a couple of small mods. The first worked reasonably well but tended to cause oscillations on carpet and rug leaving tracks of chatter marks. Admittedly the originals did leave a few but not so many, although that may be what caused the tearing. My second mod has been in operation for over a month and does a great job with no signs of problems with the rubbers and will reduce the cost of replacement by at least 90%.
I still have 3 spare original brush guards as I always buy a lot of spares with new equipment in case they go out of production, but I have a feel;ing they won’t get used!
11s brush guard rubber
Strange.
These are Willy’s “tools” after one year of daily usage.
Hard floor and carpet : ground floor 100qm.
How about a few pics to show us your mods buddy? 
The first try I used Neoprene rubber but it was too hard so for the second try I used silicone rubber strip (£6 for 5 metres of 10mm wide x 1mm thick from e-bay).
I used scissors to cut the original rubber along the two deep grooves then fitted it back into the plastic pegs of the guard. I then reassembled the guard leaving the screws very loose. I cut a strip of silicone rubber the same length as the original and slipped it into the gap as far as the lip. Tightened the screws to hold it in place. Job done!
Its a solution. Perfect done. 
How have your side brushes stayed so straight?
This is what mine look like at weekly service time so I swap them over each week.
I bind these together with a simple rubber strap from time to time. 
Very nice👍thanks for sharing hopefully this helps someone else out.
Hello - I have this issue. Your solution is something I would like to try. I have had a look on ebay for the product in your photo but I cannot find it. Please could you provide a link? Thanks
It’s ok - I found it…I think lol
This will work.
The rest can be donated to all Robovac owners in UK! 