I'm intrigued. my understanding was that the 51% was owned by the club members - so, as long as you are allowed membership then you can purchase shares? Which means that a consortium or fan investor could run the club, as long as existing members approved. Is that how it works in Germany?
The club members do not purchase shares, the club retains/holds 51%, the associated voting and overall control in the club's name.
The club members (fans etc..) are given an opportunity to determine which way those 51% of votes are used during pre-vote ballots, ensuring protection of the club from outside investors.
Gladbach is the fifth largest in the BL with 80,000 members:
https://www.statista.com/statistics/595935/german-bundesliga-clubs-member-numbers/An example of cost and benefits to members:
https://www.borussia.de/english/borussia-fans/members/become-a-member.htmlThe other 49% of shares are able to be purchased by a consortium or fan investor.
This restricts the popularity of those shares because the club is controlled and not run to make a substantial profit, just sufficient to cover running costs and agreed transfer budgets/improvements etc..
I am not sure of what 'start state' the clubs finances would need to be and how to recover 51% of the existing shares to begin, that maybe an initial prohibiter.