Change the fluid. Drop the pan and see what you find. 150k and any maintaince records? Let me guess orignal fluid?

Since you got the thing so cheap even if you raplace the trans you are still way ahead.

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1969 280SE
2027 Ram 1500
2026 Genesis GV70
2007 Tiara 3200
1988 Egg Harbor 37
1981 Boston Whaler 17