Is oil leaking from standard transmission into my engine?

About a week ago a shop replaced my clutch and flywheel.
Driving seemed okay. I drove a lot in local side-streets; slower speeds (under 35mph) to get used to shifting; breaking in the new clutch.

Looked like things were working out okay, but a couple days ago I noticed that when I turned the ignition key the engine turned over much, much faster than usual.

Driving; shifting – everything seemed okay.

Yesterday I checked the oil level. Dipstick showed level was fine, but the oil was surprisingly darker than I’m used to.

Would they have had any reason to drain the engine when they installed the new clutch kit?? Probably changed oil? cheap oil? maybe?

I’m getting ready to change the oil and filter. I always use Mobile One for high-mileage 10-30 or 10-50.

But, will changing the oil and filter simply be masking and delaying a possible problem such as a leaking main seal??

If the main seal is bad (which should have been replaced when they installed the clutch-kit, right?) – what would the symptoms be?

thanks

1992 Toyota Pickup Truck
standard 5-speed; ½ ton
4x4; 4 cylinder; 2.4 L; 22re
Miles: 100k

 

I'm no transmission expert by any stretch, but I can't imagine any way for the transmission to leak into the engine. The clutch is in the way. Essentially, you have two, separate units: The engine, and the transmission, with the clutch connecting them. There's no way I can see that any oil could get from one to the other. Also, manual transmissions aren't known for excessively high pressure in them. Even if one were leaking, it would drain out past the clutch, dripping onto the ground. You might get some clutch contanimation, but that's about it.

As for the "dark" oil in the engine, it may be they saw that it was getting dirty, and changed the oil and filter, with a darker oil than you're used to. Maybe you drove it a bit harder than usual? There's any number of reasons for dark oil on the dip stick. I can't see any connection to a clutch replacement, though. Once you change the oil and filter for your normal oil and filter, just monitor the dipstick for the oil darkening faster than usual. It IS normal for oil to darken down as the miles add up, after all. A tank of dirty gas, driving in a dirty area, dirty air taken in, you name it.

Good luck!
Pat☺

 

Thank you so much 2ToyGuy!
Really appreciate your detailed reply.
I have some mechanical ability - general repair stuff (minor tune-up; brakes; working on drive shafts, etc, etc), the internal working of my transmission, clutch and engine have always been areas I've hesitated getting into.
Clearly I need to become more familiar with the drive train.
thanks again