Me thinks we need to create a 'PTE-liveried units in unusual locations/services'-themed thread soon.
Oh yeah, Martin Loader has picture proof of that first one too (linked below).
And ofc Northern units have ended up in Glasgow more than once, but that is a tangent of a tangent.
Looking at
scot-rail's page on the 107s, after the fleet resumed operations in 1987 after the June 1986 grounding due to axle defects, some units were transferred to Eastfield, this was followed up by all the Strathclyde units moving there in July 1988 as Ayr depot lost it's entire DMU allocation; the remaining Blue/Grey sets went across to Haymarket.
In July 1991, the remaining 13 sets (in that timeframe, the whole class had been renumbered from 107 4xx to 107 7xx, then to 107 0xx to avoid clashing with new 156s & 158s respectively) were transferred to Haymarket after 156s took over services from Queen St to Dunblane/Falkirk Grahamston that same month; they were used primarily on peak-time Edinburgh - Fife services. They lasted just over a year after that however as 101s were transferred in to replace them in August 1992 (4 sets were left in service by then).
Finally, the 117s actually arrived after these 4 last 107s had been withdrawn (the first 4 in July 1993, the latter 3 in March 1994), the last of these sets being withdrawn 3 years into the National Express era (November 1999 to be precise).
Indeed they were, they were regulars on the entirety of the Glasgow South Western, far removed from the East Kilbride/Barrhead duties their livery would (in theory) confine them to (another Martin Loader photo linked below).