The original vacuum pump on these engines has a questionable bearing design. The bearings on the drive roller are held by a plastic tray that keeps the 6(?) balls evenly spaced. Over time the plastic tray disintegrates which allows the balls to shift such that the is clearance for the balls to escape the track. Escapees fall into the timing chain cavity. You can imagine what that'll do to the timing chain. If the balls make it to the sump, there's a chance the oil pump will ingest them.

The net of the story - if you don't see 4 screw heads on the front cover of the vacuum pump; that is, if the front cover is a smooth brass expanse, invest the $300-350 on a redesigned vacuum pump with shielded bearings. At least invest in a gasket so you can confirm the plastic trays are intact.

Sadly it's not uncommon for the evaporator to leak refrigerant. By all means recharge the system but keep an eye out for decreasing cooling performance. A chemical sealer might stave off the inevitable for a year or three. Some live out their lives on recharges. The alternative is a 20 hour job to replace the evaporator. If you're lucky, it'll be a bad compressor seal. The low pressure switch on the dryer (the one without pigtails) can go bad. Prudence suggests replacing it whenever you evacuate the system. There's a color coding scheme and experts say to replace the original one with one of another color... for the pressure rating, not aesthetics

It is common for the rear suspension upper diagonal strut bearings to disintegrate long before the others do. It's a bit of a puzzle to replace these struts without taking the hub apart to remove the brake backing plate but it can be done with a little bending (and bending back) of the backing plate. Others would say to redo everything in the rear suspension in one go. That would be 4 struts per side, sway bar bushings and links, control arm pivot bushings, those bushing supporting the knuckles, 4 subframe bushings, differential rear bushings (now there's a job for you!) and differential upper bushing. That's the bulk of it if not it completely.

Are the speedometer and odometer both off or just the speedo? Are you using a GPS device as a reference? Maybe you just have high expectations

Do a search on the 606 fan and clutch conversion. Do a search also on filling the original clutch with Toyota silicone fluid.

Sixto
87 300D