Looking for solutions to recent hang-ups when assembling the 240. Any input or thoughts is greatly appreciated!

So the first predicament I encountered during the assembly process is in regards to the camshaft and intermediate sprockets. Looking over the Bentley manual, I noticed a camshaft washer that sits between the seal and sprocket. I didn't have this item in any of my labeled baggies so assumed it was misplaced or lost. I decided to purchase a new camshaft sprocket washer just to play it safe. I proceeded to install the camshaft sprocket then the intermediate sprocket and began to wonder if a washer sat in between the intermediate sprocket and its seal as well...So my questions here are...do I need the camshaft sprocket washer? Does the intermediate sprocket have a washer as well?

The second dilemma pertains to the timing belt tensioner. Along with the Bentley manual, I've been watching several videos on YouTube as references. One particular video stated that the timing belt tensioner should sit flush against the block. The new timing belt tensioner, manufactured by Gates, that I planned on using does not sit perfectly flush. It has the slightest bend to it, maybe a mm gap at the center. When tapping the tensioner lightly with a hammer, I noticed that it'll sit snug for a second but then go back to its original position.

Continuing with the assembly, I positioned all the timing marks and aligned the marks on the belt with the corresponding marks on the sprockets. After that, I rotated the engine 360 degrees, to check to see if the timing marks were still aligned, and noticed the belt sliding/slipping forward. My questions here are...is the tensioner causing the belt to slip forward? Can one of the sprockets be warped or out of tolerance causing the slip? Does the camshaft washer(mentioned above) I installed have an effect? Not sure how to go about this...

Again, any input would be appreciated!

For clarity, it's a 1992 Volvo 240

P.S. I'm replacing the timing belt with the engine still in the car. Are there any tips or tricks when doing it this way? I find it difficult to line up the markings because I'm essentially looking at them on an angle; not concentrically...

 

the belt is toothed, it shouldn't be possible to slip at all unless its way too loose, or some of the sprockets are packed with dirt so the teeth don't fit into the grooves.