the vacülation may very Well go back to eMoE. and perhaps to ME.
The following Germanic words have exclusively er :
n)euer, further, n) either, other, father, reader, hearer, a(u)nswer(e(d, water, after, fynger(s, longer, Easter, maker, wither, synners. 2. The word neighbour is occasionally spelt neygh-, neighbor. The second syllable had of course been reduced to br, bar long ago.
Other vowels in unstressed position before r were of amid-mixed or at any rate dull quality even in the 16th c. Cf. Luick HG. § 472, 589.
avenger, corner, daungiers, daunger, debter, harper, kalender and kalendar (about equally frequent), maner, manner, matter, maungier, psalter. The ending -our was shortened because it was no longer stressed in AN., hence: honur, labur. Jordan § 246, in which case o would be a natural spelling by the side of traditional ou. This o thérefore need not be entirely due to Latinizing influences. The fact that or was substituted for other endings (Jespersen 9.72), proves that, whatever its sound may have been before, the 16th c. pronunciation was undoubtedly r °r ar. Cf. Luick HG. § 589, 2. Instances with out armour(e, chambouring, counsaüours, defendour, Emperour, errourfe, executours, fauour(able, ably (reg.), gouernour, harbour, honour (reg.), inhabitours 15210, labourfeth, -ers (reg.), mediatour (3), odoures ; pastours, persecutours, saueour (3),saüiöur(e (reg.),sauour 28820,souldiour, succowfe, vapours; with o:
colored, error, fauorfable, honor (20), honorable (2), honoreth, dishonored, inheritor, labored (2), mediator, pastors, persecutor, rasor, rumor, sauior (ab. 10), traitor, trdsgressors, tutors.
As in MoE. the oa-forms are the more numerous, and in many
cases the only ones.
The forms harbour (OED.: 3—7 harber(e(n) and chambouring (OED.: OF. chambre E. 4 chamber) show that -oar had become x,9r. The spelhng stubbernes 36401 also proves that -or in this word had become r, ar.
Cf. also pülers 15211, begger (3), amicaler 27429, singuler 24024,
Note indeuor with or for original oir.