TGS: I have been heavily subsidizing my parent for about 5 years now, even without any real physiological manipulation drawing down the support is hard. Hell if they did play some games or borrowed money in my name it would be easier cut strings in one swoop.
Hmm. It sounds as though they know exactly where the line is and how to not cross it, but also how to go right up to the edge of that line. Because of long-term family dynamics it appears you don't recognize that behavior as manipulative. (It is.)
I've got a saying: never wipe butt unless you want to be treated like toilet paper.
For reasons that are probably a lot older than the 5-year subsidy, you have allowed your parent to draw the line in terms of setting your financial boundaries. It sounds to me like that isn't working for you. There are parents who *don't* expect ongoing bailouts from their children without having to be explicitly told not to expect them. In fact for most healthy parents it's a no-brainer. But as luck would have it, you were dealt a hand that includes a parent for whom that particular no-brainer isn't obvious. Your parent got to draw up your financial boundaries, and they did it in a way that was advantageous to them but kind of harmful for you. Unless you want that to continue forever, you're going to have to create what we call a healthy boundary. That's a limit on behavior you will tolerate from others. You will have to communicate this boundary and perhaps politely defend it, and you will have to alter your behavior so that whatever bad decisions your parent may continue to make (and you don't control these decisions) will not affect you.
Based on what you said, you're basically wiping butt financially. You're heavily subsidizing your parent's standard of living to compensate for some decision(s) that parent is making and to protect them from the highly predictable consequences. Because of the assistance you provide, the person you're helping is able to get by just a little bit longer without changing their behavior. There's a technical term for this behavior. It's called "enabling".
At the moment, your parent is taking advantage of you. You know it, but after five years you haven't been able to dial it down to zero. Surely by now you recognize that the pattern is going to continue the rest of your life unless you find a way to fix it. Change isn't going to come from your parent's side, unless of course the subsidy gets bigger. Your parent knows exactly how far they can go without gouging you in a way that provokes you to halt the gravy train, but they're perfectly willing to continue the smaller-scale chiseling and gouging right up to that point (without regard to the financial or emotional effect on you).
The solution, which I believe you already know, is a two-part one. First, you limit the extent to which your parent's budget imbalance affects you. You get your name off any leases, loans, or other financial commitments involving them. Second, you set an end date for the support that is reasonable. It should be one that allows your parent time to adjust his or her standard of living to something sustainable. Scaling down a standard of living isn't usually an overnight process. It takes time to sell a house or to finish a lease. Depending on what cutbacks have to be made you can set a time limit.
Part of you may believe that unless you give in again or continue to subsidize you will lose that parent or suffer irreparable harm to the relationship. Your belief probably has a basis in fact, however it isn't completely true. There may be a tantrum, there may be a meltdown, and there may be a change in how your parent treats you, but the parent/child connection will not actually be broken simply because your parent learns to wipe their own butt. The relationship will change and your parent will (necessarily) become more independent. If the reasons behind that parent's dependency have to do with illness or disability, it's reasonable for you to put forth the effort to line your parent up with social and charitable services that are set up to help. If your parent balks at requesting or receiving charity, you should probably point out that they have had no problem requesting and accepting it from you, but you can't carry the load alone anymore and it's time to spread the burden across a bigger group of people. Your parent will probably have a big emotional reaction to the fact that they ARE a burden to others financially because of their refusal to either pull their own weight or do what they can to make the load lighter... especially if you or others have been telling them for years that it's "no problem". It is a problem and it's time to say so.
TL;DR version: There needs to be another line drawn. By you, this time.