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Funky brake behavior?

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I've been sold on Dot 5 brake fluid since I fitted it to my MGB when it was just new on the market back in the 70's. A friend owns my old MGB and had to rebuild the master just last year. The system hadn't been touched since I rebuilt it and there had never been bit of trouble with it in all those years and over 100K miles.
I am now beginning to wonder about it since I just tore down my BE master and discovered the rubber seal's had all swollen enough so that I believe they were covering the bleed back hole and causing my brakes to not release.
I did have a clutch failure that caused a replacement of fluid. Some of that was borrowed from a friend who assured me that it was dot5. So now I'm wondering if anyone else has had problems with dot5 or knows of similar problems had by others from its use? I really don't want to completely evacuate the system and change to dot4 since this system was completely rebuilt only about 10 years ago.

Kurt.
 
I've been told that DOT5 isn't great for the break pressure switches that are used on a Bugeye -- my Bugeye has DOT5 in it from a previous owner, and the switch only lasted a year or so. I'll be switching to DOT3/4 when I redo the system as part of the restoration.
 
When I had brake issues with my '69, it turned out to be a bad brake hose.
 
I thought you guys would appreciate an update. The answer: all of the above.

The brake warning light switch was closing off one side when bleeding.
The brake light switch was preventing complete push rod return.
And the reservoir breather hole was clogged.
 
Glad you solved the problem. What fluid are you using?
 
Dot 4.1 (I think). They have changed the labeling on the bottles around here so much that you have to read the eensy-weensy fine print to figure out what you are using.
 
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