2005 LEXUS GS430 gearbox concern

[HH20]

Hi all, I’ve been speaking to a dealer about a 2005 GS430 mk3, I currently have an IS250 and want to make the change. The vehicle looks fine for us age and 90k miles but a bit of the advert concerns me.. “This vehicle has an intermittent slight rumble from the gearbox in 5th and 6th gear when traveling at 30 miles per hour.” My first thought is that the car shouldn’t be in those gears at 30mph? Surely the engine would be labouring at that gear / speed.. but they’ve seen fit to mention the ‘issue’. Is this likely fixed by a simple fluid flush / replace despite Lexus claims that they are a sealed unit..? Or am I looking at a rare but serious problem that could lead to needing a replacement gearbox? There aren’t many of these on the road so I’d be concerned about sourcing a replacement that wasn’t silly money.. would appreciate some advice in case I could be looking at a lemon! Thanks in advance.

[The-Acre]

It could be something as simple as a transmission mount but I'd be vary wary.  I would want a transmission specialist to confirm before I parted with my money. Also a rumble sounds far more serious than a vibration. Mine can find itself in 6th at that speed on flat surfaces, certainly 5th.  Caution needed here I think.

[m4rkw]

Ask if it's ever been serviced. Flushes are not generally recommended, at 90k it should have been serviced at least once.

[Mihanicos]

Vibrations and noises are transmitted through the body of the car. Like another member already mentioned, I would check all engine and transaxle mounts,  use a small crowbar to lever the rubbermounts and suspension bushings. Also all rubber propeller shaft  couplings  transaxle and final drive.

Change the transaxle fluid and the filter. The owner's manual may state that the gearbox is sealed for life but if you look at the car's Toyota repair manual  you will find when you should change the oil and the filter. On some models, if my memory serves me right, an oil  change is recommended after about six years or 60 000 miles, whichever comes first.

Chris.