If it can roll both directions, and especially if you can get it to stop, then your V osc. is probably fine. Lack of lock is usually lack of sync in that case. Since you have H sync the sync sep is probably somewhat functional.
My first step would be to change out all the parts that couple the sync sep to the V osc. and verify the values of what is in there now against the schematic while doing so. If your set matches the below schematic R-44,45 and C-47,48, 140
http://earlytelevision.org/images/mo..._VT71_TS4J.jpg
I don't see how the osc could run and at the same time cause the sync issues so if those parts are not the problem look for weak sync sep output next.