Condo owner expanded their garden unit into common elements

[Gonzalo Escobar]

This is regarding a 13 unit building in Illinois that went condo in 1979. The building has 12 above ground units and a single garden unit. 

In the 1979 condo declarations the garden unit is listed as a 1 bedroom with a 4.4% ownership interest. The next smallest unit, six one bedrooms all are 808 sqft and have 6.4% ownership.

The garden unit is now magically the largest unit in the entire building a 1700 sqft 3 bedroom 2 bath, but continues to pay the pittance of the declaration stated proportionate share for their monthly HOA and special assessments.

I think what happened is that when the building went from boiler to central air heat, the owner of the garden unit expanded their condo into what was previously the common area basement that held the boiler. 

The unit has sold several times since this happened, but the current owner is now always demanding that the building pay for his insurance deductible on all these water issues he has had. He is refusing to pay his pittance of an HOA until his deductibles are paid.

What options does the association have?