Why should OC pay for upkeep of sole-use terrace?

Iin our scheme one lot has a terrace which it alone enjoys the use of. Access is only available through that lot.

The OC  however is milked for its upkeep. From my reading of the history of the scheme, there is no written reference  at all to the terrace. At any time. No mention of the CPRBL or who’s to maintain the terrace. The financial statements I inspected show that the OC has paid to maintain the terrace in 6 out of 7 cases of repair. (The bulk of the cost of R&M was paid by the OC).

My questions are:

(1) The OC has assumed over the years that the terrace is common property and while only one lot can use it, the OC has funded R&M.

(i) Is this fair? If not, what can we do?
(ii) Is there anything stopping the OC deciding to build another access point to the terrace so other owners, i.e. those who’ve footed the tab for decades, could enjoy that common property? (Currently the only way to access the terrace is via the lot that uses it); and

(2) Is it to the OC’s advantage to create a CPRBL that stipulates the lot enjoying sole use of the terrace is to be given “exclusive use” of it? The logic being that if they have “exclusive use” – like in the air cond situation – then that lot must pay for its upkeep. If not, how do we force the lot to be responsible for R&M?