[71Dually]

Forcing with a pry bar can potentially damage parts you don't want damaged, like bending a backing plate. Try the old hammer chisel trick on the rounded wheel cylinder bolt.

Is it possible to remove the backing plate from the spindle to gain better access to the wheel cylinder bolt? That would be my preferred way to go to access and remove that pesky rounded bolt.

Regarding a seized flare nut to brake hose connection there are four methods you can use to loosen this type of connection. The methods are penetrant, impact, grinding and heat. I would use them in that order and only use heat as a last resort as brake fluid is flammable. It's flashpoint is not like gas or alcohol but it is flammable so take necessary precautions when using any open flame heating operations.

Use only flare nut wrenches to help prevent rounding off both fuel and brake line flare nuts.

After allowing the connection to soak in penetrant position both wrenches so you can "squeeze" them together like plier handles to loosen the nut. This provides better leverage and control then trying to push or pull them "apart". It also helps maintain proper wrench orientation on the fittings to prevent rounding. if necessary you can lengthen the wrenches by using the box end (or closed end as you call it) of a wrench on the open end of the wrenches on the fittings. Same principle of using a pipe on a breaker bar to get more leverage. Again use the squeeze method for better leverage.

The following is a two person job. Presuming you have cut the rubber hose to remove the backing plate from the spindle you can get a box end on the rubber hose fitting near the brake line flare nut for a better grip. Get a hammer or another "anvil" type device and hold it tightly against one side of the hoses fitting connection where the threads are. Using another hammer impact the opposite side of the connection. You are basically trying to impact the exterior portion of the hose connectors threaded portion by smacking that between the 2 hammers. At the same time as one person smacks the connection another individual applies firm even wrench pressure until the flare nut connection breaks loose.

It is necessary to impact the threaded portion of the hose connection but be careful to not hit it so hard as to deform the fitting as that will also deform the flare nut and brake line at the same time since they are both hollow and can collapse. Only hit it hard enough to break the connection loose.

Next comes grinding. You basically grind a section of the material away on the hose connection until you just reach the outermost part of the flare nut thread. You will only need to grind a section and not the whole fitting. You are only trying to create a "crack" the length of the threads in the hose fitting that will weaken and then allow the connector to expand when the flare nut is turned. Creating an additional crack on the opposite side of the connector will aid in expansion if necessary. Be careful to not grind so far as to damage the threads on the flare nut.

Try a practice run on a nut and bolt to familiarize yourself with the process and concept by grinding the nut down to the bolt threads. That way you will see what the "break-thru" process looks like when you approach the top most portion of the bolt threads. If the nut spins on the bolt during the practice run secure it with another nut by tightening the nuts against each other on the bolt. Remember to only grind down to the very edge of the threads on the fastener you need to retain so they are not damaged. This grinding method is the same concept as using a nut splitter but like a box end wrench you are not able to put a nut splitter on hose connection fitting

The last alternative is heat but be careful as brake fluid is flammable so have an extinguisher close by. Most likely this method will not be needed as I've always found the grinding method works. Using a torch heat the hose connection at the threaded portion a dull red hot and the flare nut will loosen right up. Only heat the hose connection as heating the flare nut could damage it.

The four methods (penetrant, impact, heat and grinding) are basically breaking the grip that rust has on the threads of the two separate parts. If none of these work to separate the flare and brake hose you may need to get a new piece of straight brake line and bend a new line up. You'll need a double flare tool and a tubing bender to do this. You may not use these tools often but they are handy to have when working with both fuel and brake lines.

Rust in brake line connections could indicate rust inside the brake lines as well. I agree with 72bowtiestepper that you don't want to take chances with your brakes and you should assess if your brake lines need replacing. Also agree that yes use grade 8 fasteners on brake components. And as Daner has pointed out do not twist the hard steel lines.

Hope these methods will assist with your conundrum. Good luck.