replacing 70 year old shower pan, do I need to take out the curb?

[Lois Lane]

The shower pan on my all tile 70 year old shower started to leak. I have access the the underside of the shower and am also replacing the old galvinized pipes which are rusted through, in fact this is what alerted me to the pan leak. I want to replace just the pan and the drain. The wall tiles look great. Took out the floor tiles and first two rows of wall tiles, the pan and the subfloor. The stud walls and the floor joists are fine. Due to it's age there is of course no waterproof membrane just a layer of what looks like thick tarpaper under the 4 -5 inch mortar bed. No gravel or visible weep holes on the drain. I don't really want to remove the entire curb. The curb does not seem to be the area that was leaking, and seems to be all mortar or mortar over brick, and is quite tall and thick. I will of course have to use different tiles to finish this, unless I can find some matching 4 inch 1950's baby blue!

I understand conventional modern shower pan would require subfloor, tarpaper, preslope mortar bed, PVC membrane up the walls and over the curb, mortar bed, and finally tile set in thinset and grouted. I would like to avoid replacing the curb, which is quite tall. How did people in the 1950's keep their shower pans from leaking for 70 years without PVC? Can I run the PVC just to the top of the curb (I know, sacrilege, but it worked without any waterproof membrane for 70 years). I have posted this on another forum as well. Thanks for your help.

 

[Tile Marble Granite]

Send some pictures if you could.
Water leakage speaking, back in the days they did not have the technology to waterproof the showers. Therefore, they used bitumen (hotmop) as waterproofing.

 

[Huddersfield Tiling]

Pics please. They would be very helpful.