forester2002s

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.

If the starter-solenoid 'clicks' when you try to start, that means that the clutch-pedal has been depressed and is working as it should.

I missed that in your original post. So it's new starter, and it 'clicks'. That suggests that it is trying to connect 12V from the battery to the starter. Try measuring the voltage at the 12V terminal (the large heavy-duty cable) on the outside of the starter. There should be 12V here at all times.

Does the starter-motor 'click' once when you try to start? If so, it could be worn contacts in the starter-solenoid.

Make sure that your AAA membership is up-to-date, so that you can get a tow if you get stranded. These more modern designs, using CAN-Bus, are akin to fly-by-wire. They can play-up at any-time, and are a nightmare to debug. Sorry, but I can't be of more help.

Could also be the rear driveshaft, especially if you get a vibration under load.

On my 2002 5MT Forester, I just use 80W90 non-synth, whichever brand is cheapest. Never had a problem with the gearbox.

Welcome to the USM Board!