forester2002s

Flakey ignition-switch?

Sounds to me like the rear drive-shaft, even though you've said that you have checked it. They are difficult to check by hand, but can you get a crowbar on it to see if it's loose?

Low compression reading? And same reading on all four cylinders? I would suspect a problem with the compression gage itself.

Could be lack of fuel? Either low tank level, or something else related to fuel?

You shouldn't need a heavy-gauge wire to energize the solenoid. 16ga would work. And we're only talking about a few seconds anyway.

For a quick test of the starter: - disconnect the small-gage wire that connects to the starter solenoid-terminal; - connect a wire to the positive battery terminal; and touch the other end of the wire briefly to the starter-solenoid terminal. This will put 12V to the solenoid, and should energize the starter itself. But be aware that the test-wire from the battery will be unfused, and capable of conducting a larger than intended current.

On most models, all the warning lamps are tested during start-up: - turn the key to the ON position (just prior to turning the key to START the engine); the display should show all warning lamps illuminated, including the check-engine-lamp; this verifies which warning lamps actually work (or not).

Seized rear-diff?

Recently filled-up with (bad) gas?

10%? That seems way too large a difference.

Could be a CV-joint, especially if the vibration seems to be from one wheel only. And more likely a front CV-joint, as you say that the steering wheel shakes. Or could be the universal-joint and/or support-bearing on the rear drive-shaft.

If it has a cracked head, the coolant likely leaks, and it may have a history of overheating. Beware!

Does the car still have the original engine?

Aside from the same-diameter situation, I would expect that (or at least not-be-surprised if) on-highway driving performance would be affected. I'm thinking that different manufacturers would have their own preferred tread-design and configuration of internal metal/fabric plies. Just how any of this might affect emergency swerving or braking, or cold-weather grip, is an open question. Personally, I wouldn't risk it.

Could it be a problem with the wiring between the speed sensor and the cluster?

A reminder: Take photographs of the old timing belt before removal, including timing marks. It will make installing the new belt easier.

For my 2017 Forester, I have received these 2 documents from Subaru Canada: - Warranty Enhancement Program CVT for 2016-2017 - 10 years or 160,000km - Warranty Enhancement for CVT Park Range Switch - 8 years (2013-18 various models, no mention of Ascent)

Changed the belt and the noise went away? Maybe it's not the belt, but the tension that changed? That squeak sounds like a bearing noise to me.

Sometimes a bad ground can cause electrical mayhem. May or may not be related to your problems.

The problem might not be with the sensor itself, but with the wiring/plugs that connect to the sensor.

Have you checked for any DTCs (Diagnostic Trouble Codes), using an OBDII scanner?

Maybe time for a transmission oil change?

Personally, I would go for the 2010 EJ. That's because I do all my own maintenance, and the EJ is easy to work on. Replacing EJ headgaskets is doable for the DIY-type of owner. Maybe the 2012 FB feels nicer/newer, and drives smoother/quieter; but if something goes wrong, it will be more difficult to work on. And don't get me started about CAN-Bus. I think that both the 2010 EJ and the 2012 FB have CAN-Bus computers and wiring. A nightmare for the DIYer! If you want to get a headache, read this: CAN bus on Wikipedia

Coolant full? Then leaking on ground after driving? Then coolant-overflow reservoir is empty? Unfortunately, this sequence points to an EJ head-gasket failure.

Easy enough to do a quick check, by removing a spark plug. If the engine is flooded, the spark-plug would be wet with fuel.