All Flexicover policies purchased here on MSM exclude claims relating to pre-existing medical conditions. At the time of purchase there is a declaration that you have to tick to say that you have read and understood that you will not be covered for claims arising due to an existing medical condition. As long as you are happy to purchase cover on this basis then you would be able to apply for a Flexicover policy.
You may be able to secure cover for this condition with another product or insurer so please do consider the potential costs before making an informed decision.
Hope this helps