98 merc 200efi, when putting lower unit back on i can get the shifters back together but sometimes i wont have reverse i take it off and try it again and wont have forward i put it back together kinda close an had all 3 gear positons, yesterday and had all gear but when id put it in gear lower unit would sound like it didnt engage all the way but prop still spun, bad clutch dogs? Never had problem shifting b4 impeller change

Sounds like you are one notch off. Have you tried installing in neutral? I have found a lot of times that I will bump the shift shaft on the lower when re-installing and it will pop out of gear. Usually if you have a bad clutch dog it shows up in reverse. I got by for a while by adjusting mine a little more to reverse at the motor but eventually I had to have the clutch dog machined.

Ok thank you! About how much that run to repair?

Easy to damage the shift shaft or shift dog pin. Have seen it several times by guys trying to save money.