[COLOR="DarkRed"]I have the original internal-bias thermstat and the two internal connections have connectivity but the outer do not.[/COLOR]
Use a higher meter scale for the outer connectors. This is an internal heater that is turned on when lower heat settings are used. They are usually in the 5,000 to 10,000 ohm range.
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More importantly could there be something else wrong that is causing a ripple effect?[/COLOR]
Could be a coincidence but I doubt that.
Did you clean/check your vent system when you replaced the thermal fuse?
This is the most common cause of it blowing.

[COLOR="DarkRed"]Am I looking at flushing money where more and more will continue to blow out or go wrong?[/COLOR]
With a blown thermal cut-off other things should be checked before replacing it.

Check the heating coil.
Unplug the unit and both wires to the coil.
Check it with a meter, should be around 10 to 12 ohms.
Then check from each side of the coil to the case/frame, both should be infinite ohms (open). If not the coil may have sagged or broken and is touching the case. This can cause it to run on high and the thermostats cannot regulate it so the thermal cut-off blows.

The hi-limit should have regulated the temperature so the fuse did not blow, that is why there is a new one with the thermal cut-off..
Note: That unless there is another problem in the unit the hi-limit should never have to open. It is just a safety device with the fuse being a backup safety device.

Just in case it is not a grounded element.
With all the below the high limit will also have to be replaced.
Check that the belt is OK.
Check the seals (drum etc) in the unit. The air is pulled over the heating coils, through the drum and pushed out the exhaust. So any large seal leak will pull in room air and the cycling thermostat on the blower will run the unit hot.
Check that the lint filter is not coated with fabric softener residue which greatly reduces air flow.
Check/clean your vent system.
Check/clean the blower wheel.

If all OK you may want to replace the cycling thermostat as it's contacts may not be opening (welded shut)