You are really going to have to start with a thorough cleaning.
Strip off everything removable. Top, seats, insulation boards and padding...
Then go after it with a scraping tool/flat bladed screwdriver to bust up the compacted filth in all the cubby boxes and crevices.
Then shop vac all the dirt, top snaps, and shell casings.
Sift through it to save all the bolts and parts...you will see why later.
Then, after that, you can use the garden hose/pressure washer and a good scrub brush and purple green of your choice to scrub it back to clean CARC.
Along the way, you will become more familiar with the machine and find broken and missing items.
Once you have it clean, you can do a complete visual inspection top AND bottom and I do a photo survey of everything to document condition and use to study online. It really helps in getting to know your rig. Then do the complete PMCS services