Rhotic Accents in the UK

the oldham accent is rhotic, but is kind of the wrong side of manchester to be rhotic?

Well, it's rhotic in Blackburrrrrrrrrrrn and Burrrrrrrrrnley to the north of Manchester, and Oldham's just north of Manchester, so maybe it's on TEH RHOTIC FRONTIER.

rochdale is kind of in the way for the above theory. it kind of hangs on whether there is a rhotic strand going through bury and...whitefield?

"The interviewees talk about toilets and the van that used to come around the houses in Oldham and collect the sewage. Fred Hilton amused everyone with his tale of shouting through the flaps of the outside toilets when he was a child.
....
However, many speakers in the area to the north of Manchester remain rhotic - that is they pronounce the sound after a vowel, at one time a feature of speech throughout the UK. Nowadays within England, however, it is increasingly restricted to the West Country and this small relic area of Lancashire. Listen to the way these speakers pronounce the words or, poor, paper and morning. Speakers in this part of Lancashire potentially make a distinction between the words poor and paw and likewise between porn and pawn. While for many of us the difference between poor and pawn is simply the addition of the sound, you can clearly hear these speakers using a different vowel sound for each word. This and the stereotypical vowel sound used here in the words brown and out are striking features of speech in this part of Lancashire."