Hi Morgon,

I can't add much of use to your question, but I can report that I am also unable to install early perls on Ubuntu 16 with perlbrew. This did not seem to be the case on Ubuntu 14, though I no longer have an installation around to verify. For example:

$ perlbrew install 5.12.5
[download]

Test Summary Report
-------------------
op/numconvert.t                                                 (Wstat
+: 0 Tests: 1440 Failed: 12)
  Failed tests:  104, 108, 112, 136, 140, 144, 152, 156
                160, 168, 172, 176
op/range.t                                                      (Wstat
+: 0 Tests: 141 Failed: 25)
  Failed tests:  84-95, 99-111
op/stash.t                                                      (Wstat
+: 0 Tests: 31 Failed: 0)
  TODO passed:   26
Files=1802, Tests=349166, 423 wallclock secs (17.90 usr  5.52 sys + 15
+7.80 cusr 11.04 csys = 192.26 CPU)
Result: FAIL
makefile:970: recipe for target 'test_harness' failed
make: *** [test_harness] Error 37
##### Brew Failed #####
[download]