Do I need a new transmission?

Vehicle: 1995 Buick LeSabre Custom

Mileage: 126850

Symptoms:

• Reverse not engaging
• Have to shift gears several times to get it to engage in D
• Transmission fluid leaking
• Transmission fluid appears burnt when checked with dipstick

Other symptoms, maybe related, maybe not:

• Check Engine Light on
• ABS Light on

Had it checked at AAMCO, and they said I will need a rebuilt, remanufactured, or used transmission, but am concerned about them trying to upsell me unnecessary services/parts.

If that sounds good to you, I am planning on buying a used transmission.