Having taken a call earlier today from a mate who'd bought a gk73 in bits and found the bottom engine mount snapped off the frame i thought for a laugh i'd check mine. Cracked in the same place! There is also a frame on ebay that's gone in the same place. Has anyone else had this issue on the 73 and can it be repaired?

I had same on an RGV 250 & a KR1S, both had a bottom engine mount snapped off.
I got a local engineering firm to weld the up, cost about £20 each but that was a few years ago now.
Best to get the engine out and make a jig up the same width as the rear engine mount with a similar sized bolt and some spacers then let them weld it up.

Or buy a new frame.......

Yes mate, very common on bikes that have been over at some point in their lives.
Had mine welded, took the bike to a good welder with the engine in and had it welded as it sat.

Other common problems are engine case goes behind the sprocket cover at the top right corner where the mounting pin threads in, breaks the case at the tread showing the pin.

Also on the SP the brace on the swing arm starts to crack at the welds, only seen with the wheel out.

Cheers all, looks like it's not quite scrap yet then

Just need to hunt round for a local-ish competent welder.