There's a plethora of repairs done to fix broken away clutch tubes, but there should never be any thrust load on this tube. It's just a conduit to route the cable thru the tunnel area.
Only thing i can think of is if the cable sheath in the engine bay is a little too long, then the fixing at the tranny bracket that also holds the pully to rotate the cable 180 Degrees is not adequately fixing the aft end of the sheath, then the thrust load pushes on the end of the clutch tube where it exits the firewall.
I'm getting the the point of re-installing the engine and then can check if the sheath is loading against the tube and not the aft end fixing.
Anyone been thru this already to help with this mystery ??
Inquiring minds want to know

You have to clean the tunnel out to check everything. I would as a precaution and weld a D shaped washer around tube on rear firewall if you are seeing flex. Never worry about torn out tube.

D shaped washer is nothing more than a correct hole size washer ground off on one side for the flat side of the floor pan.

Unfortunately, the realities of physics, binding at choke points & gaskets, etc. conspire to put some movement & thrust on the tubes, such that Porsche used to have a fix kit for the rear firewall punching through (IIRC Jeff Bowlsby's 914 website has the TSB on it there), although they never did anything for the forward tack welded bracket in the mid-tunnel, other than recco opening up the tunnel & welding, or using a screw band clamp through slots cut in the D-side of the tunnel wall/floor.

In addition to Mark's recco for a D-washer, &/or I'd suggest a welded plate on the outside of the firewall to reinforce that area, which is easier to do the fix without removing the interior.

Original Porsche TSB Firewall Fix Kit installed late 1970's by my guy at Hans Imports -
Click to view attachment

Screw Band Clamp fix done at the same time per their Service Bulletin -
Click to view attachment
.

I include the above for historical purposes on the old factory fix, since there are other ways to as noted by myself & mark, etc. to do this today. When mine goes in for resto/rusto/accident repair bodywork, I'll have these removed & properly welded/reinforced "while I'm in there".

Cheers!
Tom
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There are forces put on the clutch tube, find the center tunnel photos and you will see the geometry.

You must be mis-remembering Tom, there is no factory fix kit, no Factory Service Bulletin, or bulletin of any kind, for a clutch tube repair.

The repairs done on the car in the photos...is unbelievable and I'glad you plan to redo. That's choosing my words carefully.

See this for an easy, sanitary and durable repair -courtesy of Mike Mueller's skills with a welder

Jeff has the right idea. The reason there is a guide tube for the clutch cable in the first place is that its path in the tunnel needs to be constrained so as to not interfere with the gearshift linkage, etc. This photo of the inside of the center tunnel, which is from a previous post by someone else shows this quite clearly:

Click to view attachment

The clutch cable guide tube is the slightly larger diameter tube running from its anchor point on the right near the far end toward its exit point at the near, firewall end and on the left-hand side. The bend in the middle means that when the clutch is depressed and there is tension on the cable, there are forces tending to straighten this bend, and consequently significant friction between the cable and the guide tube, which tends to pull the tube forward along with the cable.

This is also the reason that the clutch will seem to lose travel and fail to disengage if the guide tube's forward anchor point comes loose, even if the cable and the rear anchor point are both still OK. In this case, the first inch or two of clutch pedal travel just bends the guide tube to straighten its path slightly rather than moving the clutch throwout lever, because without both ends of the tube firmly anchored less force is required to flex the tube than to disengage the clutch.