It would be best to time properly using a timing light.

Try TDC or even 5BTDC at idle (700rpm) with vac retard line disconnected and plugged. Then rev engine up to 3000rpm and check what the timing is there. It should be about 25-30 BTDC. This will show if the mechanical advance is working. Sometimes the centrifugal weights get stuck.

Without a light, I would use a vacuum gauge on the intake manifold as MP suggested. Tee into line to MPS or use one at back that goes to door locks etc. Rotate distributor to position that give max vacuum, the maybe back off just a hair.

BTW - Assuming this car has 4.5L D-Jet engine! If not ignore my post and several others

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5