I bought some new nozzles, but

I bought some new nozzles that r not identical to the original e3d style.
The stem is about 4mm shorter than the orig.
I like them because they do not have a flat spot on the face that I think is causing issues.
I like they way it works, ONLY problem is sealing the PLA in.
Because of the short shaft it will not butt against the barrel to seal.
I have not disassembled to see if I can screw the barrel in another 4-5mm to get the proper seal but if I can I may not have any heat break left.

Is there another method I can use to seal it or do I have to abandon these?
any other ideas?

The flat spot on the face is the nozzle is there to smooth the filament down as it extrudes. You generally extrude wider than the filament nozzle, so you need the flat area to smooth the extrusion down properly.

I think you'd need to get something machined if you want to use your new nozzles. Either that or put some form of insulation inbetween the heater block and the heatsink - you might get a few more mm if you can insulate it.

first make sure the guide-Tube that threads into heater-block is All the way into block.
there may be enough threads left on tube to compensate for shorter nozzle

then adjust to proper height by moving to tube down

the replacement tubes, we got on eBay for our CTC, have threads on the complete length of tube,
allowing much more adjustment

See pic:

Attachment 7260