92 230CE keeps slipping out of 5th gear. Is this a bad sign, I will be changing the fluid this weekend, 1st thru 4th are very smooth

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'05 Ford Escape 100,000 miles
'87 560SL 92000 miles
'89 300TE 199,000 miles
'02 Audi TT 100,000 miles
'00 Ford Excursion V-10 121000 miles
'92 Mercury Capri 100000 miles
'02 BMW 325XI 60000 miles
'92 230CE 160000
'87 BMW 535SI 160,000 miles
'93 Rinker Captiva 209
5 Kids
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1 Wife