unless you're restoring this car and want it original,
we recommend replacing the stock 'vacuum harness' with new lines and a 'vacuum block' of some sort
the original plastic components have degraded as you have discovered,
and trying to patch it will likely keep you chasing further issues and potentially damaging your engine..
Splicing the plastic lines with rubber lines will only create other vacuum/pressure leaks, ask me how I know, go ahead, ask...
It is not really difficult, more time consuming than anything, think of it as putting together a jigsaw puzzle.
The directions will be the same weather you decide to install a vacuum block or repair your original lines (Not Recommended as a Long Term Fix)
1)Install a vacuum block and start by running vacuum lines to each component shown that receives engine vacuum.
(FPR, Baro Solenoid, Wastegate Solenoid, Purge Solenoid, Boost Gauge (if equipped)
2)The next step is to run vacuum from the above listed Solenoids to the component being controlled.
(Map Sensor, Wastegate, Charcoal Canister)
3)Next would be running the miscellaneous lines to/from the Throttle Body, Cruise Control, Turbo, Air Cleaner Housing etc.
You are going to need vacuum hose (5/32" and 7/32"), vacuum fittings, and reuse any check valves/orifices from your original system.
I can walk you through this and explain the vacuum diagram step by step on site if you like, however, I will not be back home until Monday or Tuesday.
INSTALLING A VACUUM BLOCK
There is someone on the site that knows where to buy rolls of polyline and fittings that would be similar to what is on the car from the factory if you are looking to replace that way, unfortunately I do not remember who it is but if they see the thread I am sure they will post.